Harden masking fallback and frame readers after flow sync

Co-Authored-By: brekotis <93345790+brekotis@users.noreply.github.com>

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "telemt"
-version = "3.4.12"
+version = "3.4.18"
 edition = "2024"
 
 [features]
@@ -27,6 +27,7 @@ crc32c = "0.6"
 zeroize = { version = "1.8", features = ["derive"] }
 subtle = "2.6"
 static_assertions = "1.1"
+ml-kem = { version = "0.3.2", default-features = false, features = ["alloc", "zeroize"] }
 
 # Network
 socket2 = { version = "0.6", features = ["all"] }
@@ -90,6 +91,7 @@ tokio-test = "0.4"
 criterion = "0.8"
 proptest = "1.4"
 futures = "0.3"
+tempfile = "3.27.0"
 
 [[bench]]
 name = "crypto_bench"

README.md

@@ -4,13 +4,13 @@
 
 [🇷🇺 README на русском](https://github.com/telemt/telemt/blob/main/README.ru.md)
 
-***Löst Probleme, bevor andere überhaupt wissen, dass sie existieren*** / ***It solves problems before others even realize they exist***
-
 > [!NOTE]
 >
-> Fixed TLS ClientHello is now available in official clients for Desktop / Android / iOS
+> From June 5th, 2026: we are already analyzing the causes of a new wave of "malfunctions"
+> 
+> Telegram Clients TLS ClientHello has been banned by JA3 Fingerprint: we are already looking for ways to solve this problem
 >
-> To work with EE-MTProxy, please update your client!
+> You can try build your client with our Telegram Devlibrary - [tdlib-obf](https://github.com/telemt/tdlib-obf)
 
 <p align="center">
   <a href="https://t.me/telemtrs">

README.ru.md

@@ -1,57 +1,52 @@
 # Telemt — MTProxy на Rust + Tokio
 
-[![Latest Release](https://img.shields.io/github/v/release/telemt/telemt?color=neon)](https://github.com/telemt/telemt/releases/latest) [![Stars](https://img.shields.io/github/stars/telemt/telemt?style=social)](https://github.com/telemt/telemt/stargazers) [![Forks](https://img.shields.io/github/forks/telemt/telemt?style=social)](https://github.com/telemt/telemt/network/members) [![Telegram](https://img.shields.io/badge/Telegram-Chat-24a1de?logo=telegram&logoColor=24a1de)](https://t.me/telemtrs)
-
-***Решает проблемы раньше, чем другие узнают об их существовании***
+[![Latest Release](https://img.shields.io/github/v/release/telemt/telemt?color=neon)](https://github.com/telemt/telemt/releases/latest) [![Stars](https://img.shields.io/github/stars/telemt/telemt?style=social)](https://github.com/telemt/telemt/stargazers) [![Forks](https://img.shields.io/github/forks/telemt/telemt?style=social)](https://github.com/telemt/telemt/network/members)
 
 > [!NOTE]
 >
-> Исправленный TLS ClientHello доступен в Telegram для настольных ПК, Android и iOS.
+> Клиенты Telegram подвергаются блокировке по JA3-отпечатку; мы ищем варианты решения этой проблемы
 > 
-> Пожалуйста, обновите клиентское приложение для работы с EE-MTProxy.
+> Вы можете попробовать собрать свой клиент с нашей Telegram Devlibrary — [tdlib-obf](https://github.com/telemt/tdlib-obf)
 
 <p align="center">
   <a href="https://t.me/telemtrs">
-    <img src="/docs/assets/telegram_button.svg" width="150"/>
+    <img src="https://github.com/user-attachments/assets/30b7e7b9-974a-4e3d-aab6-b58a85de4507" width="240"/>
   </a>
 </p>
 
-**Telemt** — это быстрый, безопасный и функциональный сервер, написанный на Rust. Он полностью реализует официальный алгоритм прокси Telegram и добавляет множество улучшений для продакшена:
+**Telemt** — это быстрый, безопасный и функциональный сервер, написанный на Rust: он полностью реализует официальный алгоритм Telegram прокси и добавляет множество различных улучшений
 
 ## Установка и обновление одной командой
 
 ```bash
 curl -fsSL https://raw.githubusercontent.com/telemt/telemt/main/install.sh | sh
 ```
-
 - [Инструкция по быстрому запуску](docs/Quick_start/QUICK_START_GUIDE.ru.md)
-- [Quick Start Guide](docs/Quick_start/QUICK_START_GUIDE.en.md)
 
-Реализация **TLS-fronting** максимально приближена к поведению реального HTTPS-трафика (подробнее - [FAQ](docs/FAQ.ru.md#распознаваемость-для-dpi-и-сканеров)).
+## Функционал
+Наша реализация **TLS-fronting** одна из наиболее глубоко отлаженных, продвинутых и почти поведенчески неотличима от настоящего: мы уверены, что сделали это правильно - [см. доказательства в нашей проверке](docs/FAQ.ru.md#распознаваемость-для-dpi-и-сканеров).
 
-***Middle-End Pool*** оптимизирован для высокой производительности.
+Наша архитектура ***Middle-End Pool*** в стандартных сценариях самая производительная, по сравнению с другими реализациями подключения к Middle-End прокси: не кардинально, но достаточно
 
-- Поддержка всех режимов MTProto proxy:
+- Полная поддержа всех официальных режимов MTProto proxy:
   - Classic;
-  - Secure (префикс `dd`);
-  - Fake TLS (префикс `ee` + SNI fronting);
+  - Secure — с префиксом `dd`;
+  - Fake TLS — с префиксом `ee` + SNI fronting;
 - Защита от replay-атак;
-- Маскировка трафика (перенаправление неизвестных подключений на реальные сайты);
-- Настраиваемые keepalive, таймауты, IPv6 и «быстрый режим»;
+- Опциональная маскировка трафика: перенаправление неизвестных подключений на реальные сайты;
+- Настраиваемые keepalive, таймауты, IPv6 и "быстрый режим";
 - Корректное завершение работы (Ctrl+C);
-- Подробное логирование через `trace` и `debug`.
+- Подробное логирование через `trace` и `debug` с помощью `RUST_LOG`.
 
-# Подробнее о Telemt
-- [FAQ](#faq)
-- [Архитектура](docs/Architecture)
-- [Параметры конфигурационного файла](docs/Config_params)
-- [Сборка](#build)
-- [Установка на BSD](#%D1%83%D1%81%D1%82%D0%B0%D0%BD%D0%BE%D0%B2%D0%BA%D0%B0-%D0%BD%D0%B0-bsd)
-- [Почему Rust?](#why-rust)
+## ЧаВо
+- [Часто задаваемые вопросы](docs/FAQ.ru.md)
 
-## FAQ
-- [FAQ RU](docs/FAQ.ru.md)
-- [FAQ EN](docs/FAQ.en.md)
+# Узнайте больше о Telemt
+- [Наша архитектура](docs/Architecture)
+- [Все конфигурационные параметры](docs/Config_params)
+- [Как собрать Telemt самостоятельно?](#сборка)
+- [Установка на BSD](docs/Quick_start/OPENBSD_QUICK_START_GUIDE.en.md)
+- [Почему Rust?](#почему-rust)
 
 ## Сборка
 ```bash
@@ -63,7 +58,7 @@ cd telemt
 cargo build --release
 
 # В текущем release-профиле используется lto = "fat" для максимальной оптимизации (см. Cargo.toml).
-# На системах с малым объёмом RAM (~1 ГБ) можно переопределить это значение на "thin".
+# На системах с малым объёмом ОЗУ (~1 ГБ) можно переопределить это значение на "thin".
 
 # Перейдите в каталог /bin
 mv ./target/release/telemt /bin
@@ -73,24 +68,19 @@ chmod +x /bin/telemt
 telemt config.toml
 ```
 
-## Установка на BSD
-- Руководство по сборке и настройке на английском языке [OpenBSD Guide (EN)](docs/Quick_start/OPENBSD_QUICK_START_GUIDE.en.md);
-- Пример rc.d скрипта: [contrib/openbsd/telemt.rcd](contrib/openbsd/telemt.rcd);
-- Поддержка sandbox с `pledge(2)` и `unveil(2)` пока не реализована.
-
 ## Почему Rust?
-- Надёжность для долгоживущих процессов;
-- Детерминированное управление ресурсами (RAII);
+- Надёжность при длительной работе и идемпотентное поведение;
+- Детерминированное управление ресурсами — RAII;
 - Отсутствие сборщика мусора;
-- Безопасность памяти;
+- Безопасность памяти и меньше поверхность атаки;
 - Асинхронная архитектура Tokio.
 
 ## Поддержать Telemt
 
-Telemt — это бесплатное программное обеспечение с открытым исходным кодом, разработанное в свободное время.
+Telemt — это бесплатное программное обеспечение с открытым исходным кодом, разрабатываемое в свободное время.
 Если оно оказалось вам полезным, вы можете поддержать дальнейшую разработку.
 
-Принимаемые криптовалюты (BTC, ETH, USDT, 350+ и другие):
+Любая криптовалюта (BTC, ETH, USDT и 350+ других):
 
 <p align="center">
   <a href="https://nowpayments.io/donation?api_key=2bf1afd2-abc2-49f9-a012-f1e715b37223" target="_blank" rel="noreferrer noopener">

docker-compose.yml

@@ -10,12 +10,15 @@ services:
       - "443:443"
       - "127.0.0.1:9090:9090"
       - "127.0.0.1:9091:9091"
-    # Allow caching 'proxy-secret' in read-only container
-    working_dir: /etc/telemt
+    # Working dir uses tmpfs for caching 'proxy-secret' at runtime.
+    # Config is mounted as a directory (not a single file) so the API can
+    # atomically update config.toml via write-temp → rename within the same FS.
+    working_dir: /run/telemt
+    command: ["/etc/telemt/config.toml"]
     volumes:
-      - ./config.toml:/etc/telemt/config.toml:ro
+      - ./config:/etc/telemt:rw
     tmpfs:
-      - /etc/telemt:rw,mode=1777,size=4m
+      - /run/telemt:rw,mode=1777,size=4m
     environment:
       - RUST_LOG=info
     healthcheck:
@@ -24,8 +27,6 @@ services:
       timeout: 5s
       retries: 3
       start_period: 20s
-    # Uncomment this line if you want to use host network for IPv6, but bridge is default and usually better
-    # network_mode: host
     cap_drop:
       - ALL
     cap_add:
@@ -37,3 +38,8 @@ services:
       nofile:
         soft: 65536
         hard: 262144
+    logging:
+      driver: json-file
+      options:
+        max-size: "50m"
+        max-file: "5"

docs/Advanced_settings/TUNING.de.md

@@ -86,6 +86,9 @@ Die unten angegebenen `Default`-Werte sind Code-Defaults (bei fehlendem Schlüss
 | `[[upstreams]].weight` | alle Upstreams | `u16` | nein | `1` | Basisgewicht für weighted-random Auswahl. |
 | `[[upstreams]].enabled` | alle Upstreams | `bool` | nein | `true` | Deaktivierte Einträge werden beim Start ignoriert. |
 | `[[upstreams]].scopes` | alle Upstreams | `String` | nein | `""` | Komma-separierte Scope-Tags für Request-Routing. |
+| `[[upstreams]].ipv4` | alle Upstreams | `Option<bool>` | nein | `auto` | Erlaubt IPv4-DC-Ziele für diesen Upstream. |
+| `[[upstreams]].ipv6` | alle Upstreams | `Option<bool>` | nein | `auto` | Erlaubt IPv6-DC-Ziele für diesen Upstream, inklusive Proxy-Egress unabhängig vom Host-IPv6. |
+| `[[upstreams]].prefer` | alle Upstreams | `Option<4 \| 6>` | nein | effective `[network].prefer` | Pro-Upstream-Präferenz für die DC-Ziel-Adressfamilie. |
 | `interface` | `direct` | `Option<String>` | nein | `null` | Interface-Name (z. B. `eth0`) oder lokale Literal-IP. |
 | `bind_addresses` | `direct` | `Option<Vec<IpAddr>>` | nein | `null` | Explizite Source-IP-Kandidaten (strikter Vorrang vor `interface`). |
 | `address` | `socks4` | `String` | ja | n/a | SOCKS4-Server (`ip:port` oder `host:port`). |

docs/Advanced_settings/TUNING.en.md

@@ -86,6 +86,9 @@ Defaults below are code defaults (used when a key is omitted), not necessarily v
 | `[[upstreams]].weight` | all upstreams | `u16` | no | `1` | Base weight for weighted-random selection. |
 | `[[upstreams]].enabled` | all upstreams | `bool` | no | `true` | Disabled entries are ignored at startup. |
 | `[[upstreams]].scopes` | all upstreams | `String` | no | `""` | Comma-separated scope tags for request-level routing. |
+| `[[upstreams]].ipv4` | all upstreams | `Option<bool>` | no | `auto` | Allow IPv4 DC targets for this upstream. |
+| `[[upstreams]].ipv6` | all upstreams | `Option<bool>` | no | `auto` | Allow IPv6 DC targets for this upstream, including proxy egress independent of host IPv6. |
+| `[[upstreams]].prefer` | all upstreams | `Option<4 \| 6>` | no | effective `[network].prefer` | Per-upstream DC target family preference. |
 | `interface` | `direct` | `Option<String>` | no | `null` | Interface name (e.g. `eth0`) or literal local IP for bind selection. |
 | `bind_addresses` | `direct` | `Option<Vec<IpAddr>>` | no | `null` | Explicit local source IP candidates (strict priority over `interface`). |
 | `address` | `socks4` | `String` | yes | n/a | SOCKS4 server endpoint (`ip:port` or `host:port`). |

docs/Advanced_settings/TUNING.ru.md

@@ -86,6 +86,9 @@
 | `[[upstreams]].weight` | все upstream | `u16` | нет | `1` | Базовый вес в weighted-random выборе. |
 | `[[upstreams]].enabled` | все upstream | `bool` | нет | `true` | Выключенные записи игнорируются на старте. |
 | `[[upstreams]].scopes` | все upstream | `String` | нет | `""` | Список scope-токенов через запятую для маршрутизации. |
+| `[[upstreams]].ipv4` | все upstream | `Option<bool>` | нет | `auto` | Разрешает IPv4 DC-targets для этого upstream. |
+| `[[upstreams]].ipv6` | все upstream | `Option<bool>` | нет | `auto` | Разрешает IPv6 DC-targets для этого upstream, включая proxy egress независимо от IPv6 на хосте. |
+| `[[upstreams]].prefer` | все upstream | `Option<4 \| 6>` | нет | эффективный `[network].prefer` | Предпочтительное семейство DC-target для конкретного upstream. |
 | `interface` | `direct` | `Option<String>` | нет | `null` | Имя интерфейса (например `eth0`) или literal локальный IP. |
 | `bind_addresses` | `direct` | `Option<Vec<IpAddr>>` | нет | `null` | Явные кандидаты source IP (имеют приоритет над `interface`). |
 | `address` | `socks4` | `String` | да | n/a | Адрес SOCKS4 сервера (`ip:port` или `host:port`). |

docs/Architecture/API/API.md

@@ -103,14 +103,19 @@ Notes:
 | `GET` | `/v1/runtime/me-selftest` | none | `200` | `RuntimeMeSelftestData` |
 | `GET` | `/v1/runtime/connections/summary` | none | `200` | `RuntimeEdgeConnectionsSummaryData` |
 | `GET` | `/v1/runtime/events/recent` | none | `200` | `RuntimeEdgeEventsData` |
+| `GET` | `/v1/runtime/tls-fingerprints` | optional `limit=1..1000` | `200` | `RuntimeEdgeTlsFingerprintsData` |
 | `GET` | `/v1/stats/users/active-ips` | none | `200` | `UserActiveIps[]` |
 | `GET` | `/v1/stats/users` | none | `200` | `UserInfo[]` |
+| `GET` | `/v1/config` | none | `200` | `ConfigData` |
+| `PATCH` | `/v1/config` | sparse JSON object | `200` | `PatchConfigResponse` |
 | `GET` | `/v1/users` | none | `200` | `UserInfo[]` |
 | `POST` | `/v1/users` | `CreateUserRequest` | `201` or `202` | `CreateUserResponse` |
 | `GET` | `/v1/users/{username}` | none | `200` | `UserInfo` |
 | `PATCH` | `/v1/users/{username}` | `PatchUserRequest` | `200` or `202` | `UserInfo` |
 | `DELETE` | `/v1/users/{username}` | none | `200` or `202` | `DeleteUserResponse` |
 | `POST` | `/v1/users/{username}/rotate-secret` | `RotateSecretRequest` or empty body | `200` or `202` | `CreateUserResponse` |
+| `POST` | `/v1/users/{username}/enable` | empty body | `200` or `202` | `UserInfo` |
+| `POST` | `/v1/users/{username}/disable` | empty body | `200` or `202` | `UserInfo` |
 | `POST` | `/v1/users/{username}/reset-quota` | empty body | `200` | `ResetUserQuotaResponse` |
 
 ## Endpoint Behavior
@@ -140,12 +145,16 @@ Notes:
 | `GET /v1/runtime/events/recent` | Returns recent API/runtime event records with optional `limit` query. |
 | `GET /v1/stats/users/active-ips` | Returns users that currently have non-empty active source-IP lists. |
 | `GET /v1/stats/users` | Alias of `GET /v1/users`; returns disk-first user views with runtime lag flag. |
+| `GET /v1/config` | Returns the current editable config sections as JSON (no `access.*`) plus the revision. |
+| `PATCH /v1/config` | Applies a sparse patch to editable config sections; validates, writes, and reports restart impact. |
 | `GET /v1/users` | Returns disk-first user views sorted by username. |
 | `POST /v1/users` | Creates a user and returns the effective user view plus secret. |
 | `GET /v1/users/{username}` | Returns one disk-first user view or `404` when absent. |
 | `PATCH /v1/users/{username}` | Updates selected per-user fields with JSON Merge Patch semantics. |
 | `DELETE /v1/users/{username}` | Deletes one user and related per-user access-map entries. |
 | `POST /v1/users/{username}/rotate-secret` | Rotates one user's secret and returns the effective secret. |
+| `POST /v1/users/{username}/enable` | Enables one user, removing any disabled override from config. |
+| `POST /v1/users/{username}/disable` | Disables one user and closes active runtime sessions for that user. |
 | `POST /v1/users/{username}/reset-quota` | Resets one user's runtime quota counter and persists quota state. |
 
 ## Common Error Codes
@@ -153,6 +162,8 @@ Notes:
 | HTTP | `error.code` | Trigger |
 | --- | --- | --- |
 | `400` | `bad_request` | Invalid JSON, validation failures, malformed request body. |
+| `400` | `access_not_editable` | `PATCH /v1/config` body contains an `access` key (managed via users API). |
+| `400` | `section_not_editable` | `PATCH /v1/config` body contains `server`, `network`, or an unknown top-level key. |
 | `401` | `unauthorized` | Missing/invalid `Authorization` when `auth_header` is configured. |
 | `403` | `forbidden` | Source IP is not allowed by whitelist. |
 | `403` | `read_only` | Mutating endpoint called while `read_only=true`. |
@@ -172,9 +183,12 @@ Notes:
 | Path matching | Exact match on `req.uri().path()`. Query string does not affect route matching. |
 | Trailing slash | Trimmed for route matching when path length is greater than 1. Example: `/v1/users/` matches `/v1/users`. |
 | Username route with extra slash | `/v1/users/{username}/...` is not treated as user route and returns `404`. |
+| `DELETE /v1/config` (or any method not in `GET`, `PATCH`) | `405 method_not_allowed` with `Allow: GET, PATCH`. |
 | `PUT /v1/users/{username}` | `405 method_not_allowed`. |
 | `POST /v1/users/{username}` | `404 not_found`. |
 | `POST /v1/users/{username}/rotate-secret/` | Trailing slash is trimmed and the route matches `rotate-secret`. |
+| `POST /v1/users/{username}/enable/` | Trailing slash is trimmed and the route matches `enable`. |
+| `POST /v1/users/{username}/disable/` | Trailing slash is trimmed and the route matches `disable`. |
 | `POST /v1/users/{username}/reset-quota/` | Trailing slash is trimmed and the route matches `reset-quota`. |
 
 ## Body and JSON Semantics
@@ -205,9 +219,10 @@ Notes:
 | `max_tcp_conns` | `usize` | no | Per-user concurrent TCP limit. |
 | `expiration_rfc3339` | `string` | no | RFC3339 expiration timestamp. |
 | `data_quota_bytes` | `u64` | no | Per-user traffic quota. |
-| `rate_limit_up_bps` | `u64` | no | Per-user upload rate limit in bytes per second. |
-| `rate_limit_down_bps` | `u64` | no | Per-user download rate limit in bytes per second. |
+| `rate_limit_up_bps` | `u64` | no | Per-user upload rate limit in bits per second. |
+| `rate_limit_down_bps` | `u64` | no | Per-user download rate limit in bits per second. |
 | `max_unique_ips` | `usize` | no | Per-user unique source IP limit. |
+| `enabled` | `bool` | no | User enable flag. Missing means enabled. `false` persists a disabled override. |
 
 ### `PatchUserRequest`
 | Field | Type | Required | Description |
@@ -217,9 +232,10 @@ Notes:
 | `max_tcp_conns` | `usize|null` | no | Per-user concurrent TCP limit; `null` removes the per-user override. |
 | `expiration_rfc3339` | `string|null` | no | RFC3339 expiration timestamp; `null` removes the expiration. |
 | `data_quota_bytes` | `u64|null` | no | Per-user traffic quota; `null` removes the per-user quota. |
-| `rate_limit_up_bps` | `u64|null` | no | Per-user upload rate limit in bytes per second; `null` removes the upload direction limit. |
-| `rate_limit_down_bps` | `u64|null` | no | Per-user download rate limit in bytes per second; `null` removes the download direction limit. |
+| `rate_limit_up_bps` | `u64|null` | no | Per-user upload rate limit in bits per second; `null` removes the upload direction limit. |
+| `rate_limit_down_bps` | `u64|null` | no | Per-user download rate limit in bits per second; `null` removes the download direction limit. |
 | `max_unique_ips` | `usize|null` | no | Per-user unique source IP limit; `null` removes the per-user override. |
+| `enabled` | `bool|null` | no | `false` disables the user. `true` or `null` removes the disabled override, so the user is enabled. |
 
 ### `access.user_source_deny` via API
 - In current API surface, per-user deny-list is **not** exposed as a dedicated field in `CreateUserRequest` / `PatchUserRequest`.
@@ -236,6 +252,20 @@ alice = ["203.0.113.0/24", "2001:db8:abcd::/48"]
 bob = ["198.51.100.42/32"]
 ```
 
+### `PatchConfigRequest`
+
+A sparse JSON object containing only the top-level config sections to modify. Each key must be one of the editable sections (`general`, `timeouts`, `censorship`, `upstreams`, `show_link`, `dc_overrides`). Tables within a section are deep-merged field-by-field into the existing config; arrays and scalar values replace the existing value wholesale. Untouched sections and file comments are preserved.
+
+**Rejected keys:**
+- `access` → `400 access_not_editable` (users/secrets are managed via `POST/PATCH /v1/users`).
+- `server`, `network`, or any unknown top-level key → `400 section_not_editable`.
+- An object with no editable keys → `400 bad_request` (empty patch).
+
+Example — patch only the SNI domain:
+```json
+{"censorship": {"tls_domain": "front.example.com"}}
+```
+
 ### `RotateSecretRequest`
 | Field | Type | Required | Description |
 | --- | --- | --- | --- |
@@ -245,6 +275,31 @@ An empty request body is accepted and generates a new secret automatically.
 
 ## Response Data Contracts
 
+### `ConfigData`
+
+Returned by `GET /v1/config` as the envelope `data`. The fields are exactly the editable TOML sections. The current revision is returned in the envelope `revision` field (same value as `config_hash` in `SystemInfoData`), **not** inside `data`.
+
+| Field | Type | Description |
+| --- | --- | --- |
+| `general` | `object?` | `[general]` section, if present in config. |
+| `timeouts` | `object?` | `[timeouts]` section, if present. |
+| `censorship` | `object?` | `[censorship]` section, if present. |
+| `upstreams` | `object?` | `[upstreams]` section, if present. |
+| `show_link` | `object?` | `[show_link]` section, if present. |
+| `dc_overrides` | `object?` | `[dc_overrides]` section, if present. |
+
+Sections absent from the config file are absent from the response (not `null`). Only the editable sections above are returned; `access` (users/secrets), `server` (carries the API `auth_header` and per-node identity), and `network` (per-node addresses) are always excluded.
+
+### `PatchConfigResponse`
+
+Returned by `PATCH /v1/config` on success (`200`).
+
+| Field | Type | Description |
+| --- | --- | --- |
+| `revision` | `string` | SHA-256 hex of the config file after the patch was written. |
+| `restart_required` | `bool` | `true` when one or more changed fields require a process restart to take effect. Hot-reloadable fields (e.g. `general.log_level`) are applied automatically by the config file watcher; restart-required fields (e.g. any `censorship.*`, `timeouts.*`, `upstreams`, or `general.modes` change) are written to disk but only take effect after the Telemt process is restarted. The caller is responsible for triggering a restart when this flag is `true`. |
+| `changed` | `string[]` | Top-level section names that differed between the old and new config (e.g. `["censorship"]`). |
+
 ### `HealthData`
 | Field | Type | Description |
 | --- | --- | --- |
@@ -807,6 +862,43 @@ An empty request body is accepted and generates a new secret automatically.
 | `event_type` | `string` | Event kind identifier. |
 | `context` | `string` | Context text (truncated to implementation-defined max length). |
 
+### `RuntimeEdgeTlsFingerprintsData`
+| Field | Type | Description |
+| --- | --- | --- |
+| `enabled` | `bool` | Endpoint availability under `runtime_edge_enabled`. |
+| `reason` | `string?` | `feature_disabled` when endpoint is disabled. |
+| `generated_at_epoch_secs` | `u64` | Snapshot generation timestamp. |
+| `data` | `RuntimeEdgeTlsFingerprintsPayload?` | Null when unavailable. |
+
+#### `RuntimeEdgeTlsFingerprintsPayload`
+| Field | Type | Description |
+| --- | --- | --- |
+| `limit` | `usize` | Effective Top-N row count. |
+| `retention_secs` | `u64` | In-memory retention window, derived from `general.beobachten_minutes`. |
+| `capacity` | `usize` | Maximum retained fingerprint buckets. |
+| `dropped_total` | `u64` | Buckets dropped because the collector was full. |
+| `parse_error_total` | `u64` | Complete ClientHello records that could not be fingerprinted. |
+| `by_fingerprint` | `RuntimeEdgeTlsFingerprintRow[]` | Global JA3/JA4 leaderboard. |
+| `by_ip` | `RuntimeEdgeTlsFingerprintRow[]` | Source-IP scoped leaderboard. |
+| `by_cidr` | `RuntimeEdgeTlsFingerprintRow[]` | Source CIDR scoped leaderboard (`/24` for IPv4, `/56` for IPv6). |
+| `by_user` | `RuntimeEdgeTlsFingerprintRow[]` | Authenticated user scoped leaderboard. |
+
+#### `RuntimeEdgeTlsFingerprintRow`
+| Field | Type | Description |
+| --- | --- | --- |
+| `scope` | `string?` | IP, CIDR, or username; absent in `by_fingerprint`. |
+| `ja3` | `string` | JA3 MD5 hash. |
+| `ja3_raw` | `string` | Raw JA3 field string. |
+| `ja4` | `string` | JA4 TLS client fingerprint. |
+| `ja4_raw` | `string` | Raw JA4 material used for the hashed parts. |
+| `total` | `u64` | Complete ClientHello observations for this bucket. |
+| `auth_success` | `u64` | TLS-authenticated observations for this bucket. |
+| `bad_or_probe` | `u64` | Complete ClientHello observations later classified as bad/probe. |
+| `first_seen_epoch_secs` | `u64` | First observation timestamp. |
+| `last_seen_epoch_secs` | `u64` | Last observation timestamp. |
+
+JA3 follows the Salesforce ClientHello field order. JA4 follows the FoxIO TLS-client `a_b_c` format; GREASE values are excluded and no high-cardinality Prometheus labels are emitted for fingerprints.
+
 ### `ZeroAllData`
 | Field | Type | Description |
 | --- | --- | --- |
@@ -1165,13 +1257,14 @@ An empty request body is accepted and generates a new secret automatically.
 | Field | Type | Description |
 | --- | --- | --- |
 | `username` | `string` | Username. |
+| `enabled` | `bool` | Effective user enable flag. Missing config entry is reported as `true`. |
 | `in_runtime` | `bool` | Whether current runtime config already contains this user. |
 | `user_ad_tag` | `string?` | Optional ad tag (32 hex chars). |
 | `max_tcp_conns` | `usize?` | Optional max concurrent TCP limit. |
 | `expiration_rfc3339` | `string?` | Optional expiration timestamp. |
 | `data_quota_bytes` | `u64?` | Optional data quota. |
-| `rate_limit_up_bps` | `u64?` | Optional upload rate limit in bytes per second. |
-| `rate_limit_down_bps` | `u64?` | Optional download rate limit in bytes per second. |
+| `rate_limit_up_bps` | `u64?` | Optional upload rate limit in bits per second. |
+| `rate_limit_down_bps` | `u64?` | Optional download rate limit in bits per second. |
 | `max_unique_ips` | `usize?` | Optional unique IP limit. |
 | `current_connections` | `u64` | Current live connections. |
 | `active_unique_ips` | `usize` | Current active unique source IPs. |
@@ -1232,13 +1325,106 @@ Link generation uses active config and enabled modes:
 | `used_bytes` | `u64` | Current used bytes after reset; always `0` on success. |
 | `last_reset_epoch_secs` | `u64` | Unix timestamp of the reset operation. |
 
+## Config Endpoints
+
+### `GET /v1/config`
+
+Returns the current editable config sections as TOML-shaped JSON, plus the current revision. The `access` section (users and secrets) is always stripped and never appears in the response.
+
+**Auth:** requires `Authorization` header when `auth_header` is configured (same as all other endpoints).
+
+**Success `200` response body** (`data` field of the standard envelope):
+```json
+{
+  "revision": "<sha256-hex>",
+  "censorship": {"tls_domain": "front.example.com"},
+  "general": {"log_level": "normal"}
+}
+```
+
+Top-level sections absent from the config file are absent from the response. Only `GET` and `PATCH` are accepted; any other method returns `405 Method Not Allowed` with `Allow: GET, PATCH`.
+
+---
+
+### `PATCH /v1/config`
+
+Applies a sparse patch to the editable config sections. The merged config is fully validated before writing; if validation fails the file is not modified.
+
+**Auth:** requires `Authorization` header when `auth_header` is configured.
+
+**Headers:**
+
+| Header | Required | Description |
+| --- | --- | --- |
+| `Authorization` | when configured | Same token as all other endpoints. |
+| `Content-Type: application/json` | recommended | Not enforced, but body must be valid JSON. |
+| `If-Match: <revision>` | no | Optimistic concurrency. `<revision>` is the `revision` value from `GET /v1/config` or `config_hash` from `GET /v1/system/info`. If supplied and it does not match the current on-disk revision, returns `409 revision_conflict`. If omitted, the patch applies unconditionally. |
+
+**Editable sections:** `general`, `timeouts`, `censorship`, `upstreams`, `show_link`, `dc_overrides`.
+
+**Rejected keys and their error codes:**
+
+| Key | HTTP | `error.code` |
+| --- | --- | --- |
+| `access` | `400` | `access_not_editable` |
+| `server`, `network`, or any unknown key | `400` | `section_not_editable` |
+| Object with no editable key | `400` | `bad_request` |
+
+**Merge semantics:** tables are deep-merged field-by-field; arrays and scalar values replace the existing value wholesale. File comments and untouched sections are preserved.
+
+**Validation:** the merged config is deserialized into the full `ProxyConfig` type and validated before writing. Failures return `400` with a descriptive message; the file is not modified.
+
+**Read-only mode:** returns `403 read_only` when the API runs with `read_only = true`.
+
+**Success `200` response body** (`data` field of the standard envelope):
+```json
+{
+  "revision": "<new-sha256-hex>",
+  "restart_required": true,
+  "changed": ["censorship"]
+}
+```
+
+- `revision` — SHA-256 hex of the config file after the write.
+- `restart_required` — `true` when the change affects a field that Telemt cannot hot-reload (e.g. `censorship.*`, `timeouts.*`, `upstreams`, `general.modes`). Hot-reloadable fields (e.g. `general.log_level`) are applied automatically by the config file watcher. Restart-required fields are written to disk but only take effect after the Telemt process is restarted; the caller is responsible for triggering the restart.
+- `changed` — list of top-level section names that differed.
+
+**Status codes:**
+
+| HTTP | `error.code` | Condition |
+| --- | --- | --- |
+| `200` | — | Patch applied successfully. |
+| `400` | `bad_request` | Invalid JSON, empty patch, or config validation/deserialization failure. |
+| `400` | `access_not_editable` | Patch contains an `access` key. |
+| `400` | `section_not_editable` | Patch contains `server`, `network`, or an unknown top-level key. |
+| `401` | `unauthorized` | Missing or invalid `Authorization` header. |
+| `403` | `read_only` | API is in read-only mode. |
+| `405` | `method_not_allowed` | Method other than `GET` or `PATCH` used on `/v1/config`. |
+| `409` | `revision_conflict` | `If-Match` header supplied but does not match current revision. |
+| `500` | `internal_error` | I/O or serialization failure. |
+
+**curl example:**
+```bash
+# get current revision
+curl -s -H "Authorization: <token>" http://127.0.0.1:<api>/v1/system/info | jq -r .config_hash
+
+# patch the SNI domain with optimistic concurrency
+curl -s -X PATCH -H "Authorization: <token>" -H "If-Match: <revision>" \
+  -H "Content-Type: application/json" \
+  -d '{"censorship":{"tls_domain":"front.example.com"}}' \
+  http://127.0.0.1:<api>/v1/config
+```
+
 ## Mutation Semantics
 
 | Endpoint | Notes |
 | --- | --- |
+| `PATCH /v1/config` | Deep-merges the patch into editable config sections (tables merged per-field; arrays/scalars replaced wholesale). Validates the merged result before writing. Writes only the touched sections via atomic `tmp + rename`. Returns the new revision and which sections changed. |
 | `POST /v1/users` | Creates user, validates config, then atomically updates only affected `access.*` TOML tables (`access.users` always, plus optional per-user tables present in request). |
 | `PATCH /v1/users/{username}` | Partial update of provided fields only. Missing fields remain unchanged; explicit `null` removes optional per-user entries. The write path updates only affected `access.*` TOML tables. |
 | `POST /v1/users/{username}/rotate-secret` | Replaces the user's secret with a provided valid 32-hex value or a generated value, then returns the effective secret in `CreateUserResponse`. |
+| `POST /v1/users/{username}/enable` | Enables the user idempotently by removing the `access.user_enabled[username]` override and updating the runtime admission state immediately. |
+| `POST /v1/users/{username}/disable` | Disables the user idempotently by writing `access.user_enabled[username] = false`, updating runtime admission immediately, and cancelling active sessions for that username. |
 | `POST /v1/users/{username}/reset-quota` | Resets the runtime quota counter for the route username, persists quota state to `general.quota_state_path`, and does not modify user config. |
 | `DELETE /v1/users/{username}` | Deletes only specified user, removes this user from related optional `access.user_*` maps, blocks last-user deletion, and atomically updates only related `access.*` TOML tables. |
 
@@ -1282,6 +1468,7 @@ Additional runtime endpoint behavior:
 | `/v1/runtime/me-selftest` | No | ME pool unavailable => `enabled=false`, `reason=source_unavailable` | `enabled=true`, full payload |
 | `/v1/runtime/connections/summary` | `runtime_edge_enabled=false` => `enabled=false`, `reason=feature_disabled` | Recompute lock contention with no cache entry => `enabled=true`, `reason=source_unavailable` | `enabled=true`, full payload |
 | `/v1/runtime/events/recent` | `runtime_edge_enabled=false` => `enabled=false`, `reason=feature_disabled` | Not used in current implementation | `enabled=true`, full payload |
+| `/v1/runtime/tls-fingerprints` | `runtime_edge_enabled=false` => `enabled=false`, `reason=feature_disabled` | Not used in current implementation | `enabled=true`, full payload |
 
 ## ME Fallback Behavior Exposed Via API
 

docs/Architecture/Fronting-splitting/TLS_JA3_JA4_ANALYSIS.ru.md

@@ -0,0 +1,507 @@
+# JA3 и JA4 анализ в Telemt
+
+Этот документ описывает, как использовать JA3/JA4 telemetry в Telemt для диагностики блокировок, которые происходят на основе TLS ClientHello, особенно JA4 TLS client fingerprint.
+
+Цель документа практическая: помочь оператору понять, какой клиентский TLS-отпечаток реально доходит до Telemt, как он распределён по IP/CIDR/пользователям, и как отделить JA4-based фильтрацию от блокировки по IP, SNI, домену, server flight или активному сканированию.
+
+## Коротко
+
+JA3 и JA4 описывают форму TLS ClientHello. ClientHello отправляет клиент, поэтому JA3/JA4 в этом контексте являются fingerprint'ами клиентской TLS-реализации, а не Telemt как сервера.
+
+Telemt собирает JA3/JA4 только из уже прочитанного полного ClientHello:
+
+- без packet capture;
+- без MITM;
+- без расшифровки TLS;
+- без дополнительных сетевых чтений;
+- без Prometheus labels с высокой кардинальностью;
+- с ограниченным in-memory TTL/cap collector.
+
+Собранные данные доступны:
+
+- через API: `GET /v1/runtime/tls-fingerprints`;
+- через `/beobachten`, если `general.beobachten=true`.
+
+Основная польза:
+
+- увидеть, какие JA4 реально используют клиенты;
+- понять, один ли fingerprint страдает у всех пользователей;
+- отделить проблему клиента от проблемы IP/ASN/домена;
+- увидеть, доходят ли проблемные соединения до Telemt вообще;
+- сравнить successful TLS-auth и bad/probe поток для одного fingerprint;
+- собрать evidence для последующего изменения клиента, маршрута или deployment-профиля.
+
+## Что такое JA3
+
+JA3 - старый и широко совместимый способ получить hash от TLS ClientHello.
+
+JA3 строится из ClientHello fields:
+
+```text
+SSLVersion,Cipher,SSLExtension,EllipticCurve,EllipticCurvePointFormat
+```
+
+Значения внутри полей записываются в порядке, в котором они пришли в ClientHello. GREASE values исключаются. Итоговая строка хэшируется MD5, поэтому в API есть два поля:
+
+- `ja3` - MD5 hash;
+- `ja3_raw` - исходная строка, из которой получен hash.
+
+Практическое значение JA3 в 2026 году ограничено тем, что современные TLS-клиенты и браузерные стеки могут менять порядок extensions. Поэтому JA3 полезен как совместимый исторический сигнал, но для диагностики современных блокировок обычно важнее JA4.
+
+## Что такое JA4
+
+JA4 TLS client fingerprint - более структурированный fingerprint ClientHello.
+
+JA4 в Telemt считается для TLS-over-TCP ClientHello и имеет форму:
+
+```text
+t<version><sni_marker><cipher_count><extension_count><alpn_marker>_<cipher_hash>_<extension_hash>
+```
+
+Пример:
+
+```text
+t13d1516h2_8daaf6152771_e5627efa2ab1
+```
+
+Части JA4:
+
+| Часть | Смысл |
+| --- | --- |
+| `t` | TLS over TCP. Telemt сейчас не считает JA4 для QUIC/DTLS. |
+| `13`, `12`, `11`, `10` | TLS version, предпочтительно из `supported_versions`. |
+| `d` / `i` | Есть SNI domain (`d`) или SNI отсутствует (`i`). |
+| `15` | Количество cipher suites без GREASE, capped до `99`. |
+| `16` | Количество extensions без GREASE, capped до `99`. |
+| `h2`, `h1`, `00` | ALPN marker: первый и последний символ первого ALPN value или `00`. |
+| `cipher_hash` | SHA256 от отсортированного списка ciphers, первые 12 hex chars. |
+| `extension_hash` | SHA256 от отсортированных extensions плюс signature algorithms, первые 12 hex chars. |
+
+Важное отличие JA4 от JA3: JA4 нормализует часть полей, поэтому он устойчивее к простому изменению порядка extensions. Это делает JA4 удобным для фильтров и одновременно полезным для диагностики таких фильтров.
+
+## Где Telemt видит ClientHello
+
+В TLS/FakeTLS режиме Telemt получает первые bytes соединения и определяет, похоже ли оно на TLS handshake. Если record является полным ClientHello и проходит bounds checks, Telemt один раз парсит его для JA3/JA4.
+
+Дальше возможны три исхода:
+
+1. **Успешный MTProxy/FakeTLS клиент**
+   - Telemt принимает TLS-auth;
+   - fingerprint записывается в global/IP/CIDR scopes;
+   - после успешной TLS-auth Telemt добавляет user scope.
+
+2. **Bad client или probe**
+   - ClientHello полный, но auth не проходит;
+   - fingerprint записывается в global/IP/CIDR scopes;
+   - user scope не записывается;
+   - `bad_or_probe` увеличивается.
+
+3. **Неполный или обрезанный ClientHello**
+   - fingerprint не считается;
+   - такие случаи остаются в существующих bad-class counters.
+
+Если фильтр режет трафик до того, как TCP connection или ClientHello дошли до процесса Telemt, Telemt не увидит этот fingerprint. Это важнейшее диагностическое отличие: отсутствие fingerprint'а во время жалобы пользователя часто означает блокировку до приложения, а не проблему внутри Telemt.
+
+## Включение сбора
+
+Collector включается, когда включён хотя бы один потребитель:
+
+```toml
+[general]
+beobachten = true
+beobachten_minutes = 10
+```
+
+или:
+
+```toml
+[server.api]
+runtime_edge_enabled = true
+runtime_edge_top_n = 50
+```
+
+Практически:
+
+- для файлового/metrics endpoint анализа достаточно `general.beobachten=true`;
+- для API snapshot нужен `server.api.runtime_edge_enabled=true`;
+- `general.beobachten_minutes` задаёт retention window для fingerprint buckets;
+- `server.api.runtime_edge_top_n` задаёт default Top-N размер API snapshot.
+
+## API snapshot
+
+Endpoint:
+
+```bash
+curl -s http://127.0.0.1:9091/v1/runtime/tls-fingerprints
+```
+
+С явным лимитом:
+
+```bash
+curl -s 'http://127.0.0.1:9091/v1/runtime/tls-fingerprints?limit=100'
+```
+
+Если API защищён header'ом:
+
+```bash
+curl -s \
+  -H 'Authorization: Bearer YOUR_TOKEN' \
+  'http://127.0.0.1:9091/v1/runtime/tls-fingerprints?limit=100'
+```
+
+Если `runtime_edge_enabled=false`, endpoint возвращает payload с:
+
+```json
+{
+  "enabled": false,
+  "reason": "feature_disabled"
+}
+```
+
+### Структура payload
+
+Основные поля:
+
+| Поле | Смысл |
+| --- | --- |
+| `retention_secs` | Текущее TTL окно collector'а. |
+| `capacity` | Максимум retained buckets. |
+| `dropped_total` | Сколько новых buckets отброшено из-за cap. |
+| `parse_error_total` | Сколько полных ClientHello не удалось распарсить. |
+| `by_fingerprint` | Top fingerprints глобально. |
+| `by_ip` | Top fingerprints по exact source IP. |
+| `by_cidr` | Top fingerprints по source prefix: IPv4 `/24`, IPv6 `/56`. |
+| `by_user` | Top fingerprints по authenticated user. |
+
+Строка snapshot:
+
+| Поле | Смысл |
+| --- | --- |
+| `scope` | IP, CIDR или username. В `by_fingerprint` отсутствует. |
+| `ja3` | JA3 hash. |
+| `ja3_raw` | Raw JA3 string. |
+| `ja4` | JA4 TLS client fingerprint. |
+| `ja4_raw` | Raw JA4 material. |
+| `total` | Сколько полных ClientHello попало в этот bucket. |
+| `auth_success` | Сколько из них успешно прошли TLS-auth. |
+| `bad_or_probe` | Сколько были bad/probe после полного ClientHello. |
+| `first_seen_epoch_secs` | Первый timestamp bucket'а. |
+| `last_seen_epoch_secs` | Последний timestamp bucket'а. |
+
+### Быстрый просмотр через jq
+
+Top JA4 глобально:
+
+```bash
+curl -s http://127.0.0.1:9091/v1/runtime/tls-fingerprints \
+  | jq -r '.data.data.by_fingerprint[] | [.ja4, .total, .auth_success, .bad_or_probe] | @tsv'
+```
+
+Top JA4 по пользователям:
+
+```bash
+curl -s http://127.0.0.1:9091/v1/runtime/tls-fingerprints?limit=100 \
+  | jq -r '.data.data.by_user[] | [.scope, .ja4, .total, .auth_success] | @tsv'
+```
+
+Top JA4 по CIDR:
+
+```bash
+curl -s http://127.0.0.1:9091/v1/runtime/tls-fingerprints?limit=100 \
+  | jq -r '.data.data.by_cidr[] | [.scope, .ja4, .total, .auth_success, .bad_or_probe] | @tsv'
+```
+
+Ошибки парсинга и drops:
+
+```bash
+curl -s http://127.0.0.1:9091/v1/runtime/tls-fingerprints \
+  | jq '.data.data | {retention_secs, capacity, dropped_total, parse_error_total}'
+```
+
+## Beobachten output
+
+Если включён endpoint metrics, `/beobachten` содержит обычные forensic buckets и, когда есть данные, append-only секцию TLS fingerprints:
+
+```bash
+curl -s http://127.0.0.1:9090/beobachten
+```
+
+Фрагмент:
+
+```text
+[tls_fingerprints]
+retention_secs=600 capacity=65536 dropped_total=0 parse_error_total=0
+[tls_fingerprints.by_fingerprint]
+ja4=t13d1516h2_8daaf6152771_e5627efa2ab1 ja3=... total=42 auth_success=41 bad_or_probe=1 first_seen=... last_seen=...
+[tls_fingerprints.by_cidr]
+scope=203.0.113.0/24 ja4=t13d1516h2_8daaf6152771_e5627efa2ab1 ja3=... total=10 auth_success=10 bad_or_probe=0 first_seen=... last_seen=...
+```
+
+`/beobachten` удобен для быстрой операторской диагностики без API client. API удобнее для автоматической корреляции.
+
+## Как анализировать JA4-based блокировку
+
+### 1. Зафиксировать симптом
+
+Перед анализом нужно записать:
+
+- какие пользователи жалуются;
+- какая версия Telegram client используется;
+- какая платформа: Desktop, Android, iOS;
+- какой источник сети: mobile ISP, home ISP, corporate network, country/region;
+- работает ли тот же пользователь через другой network path;
+- работает ли другой пользователь с того же IP/CIDR;
+- видит ли Telemt новые ClientHello от проблемного пользователя в момент попытки.
+
+JA4 без контекста почти всегда недостаточен. Фильтры часто используют сочетание:
+
+- JA4;
+- destination IP;
+- SNI;
+- порт;
+- ASN/source network;
+- rate или connection pattern;
+- reputation домена/IP;
+- active probing result.
+
+### 2. Проверить, доходит ли ClientHello до Telemt
+
+Во время попытки подключения проблемного пользователя смотрите:
+
+```bash
+curl -s 'http://127.0.0.1:9091/v1/runtime/tls-fingerprints?limit=200' \
+  | jq '.data.data.by_user, .data.data.by_ip, .data.data.by_cidr'
+```
+
+Интерпретация:
+
+| Наблюдение | Вероятный вывод |
+| --- | --- |
+| Нет новых rows для IP/CIDR пользователя | Блокировка до Telemt: routing, firewall, ISP/DPI drop, IP block, SYN/TCP reset, UDP/TCP path issue. |
+| Есть `by_ip`/`by_cidr`, но нет `by_user` | ClientHello дошёл, но TLS-auth/MTProxy layer не дошёл до успешного пользователя. Возможны bad key, probe, wrong client, active scanner, обрыв после ClientHello. |
+| Есть `by_user.auth_success` | Клиентский JA4 дошёл и был принят Telemt. Если пользователь всё равно видит проблему, искать нужно дальше: relay path, Telegram upstream, quota, route mode, session cancellation, ME/direct routing. |
+| Резко растёт `bad_or_probe` для одного JA4 | Вероятны сканеры или неправильные клиенты с тем же fingerprint family. |
+
+### 3. Сравнить working и blocked случаи
+
+Снимите snapshot во время working case и blocked case:
+
+```bash
+curl -s 'http://127.0.0.1:9091/v1/runtime/tls-fingerprints?limit=500' > tls-fp-working.json
+curl -s 'http://127.0.0.1:9091/v1/runtime/tls-fingerprints?limit=500' > tls-fp-blocked.json
+```
+
+Сравните:
+
+- появился ли тот же `ja4` в blocked сети;
+- меняется ли `ja4` между версиями клиента;
+- меняется ли только IP/CIDR при том же `ja4`;
+- есть ли `auth_success` для того же `ja4` из других сетей;
+- отличается ли `bad_or_probe` между сетями.
+
+Ключевая матрица:
+
+| Working JA4 | Blocked JA4 | Вывод |
+| --- | --- | --- |
+| Same | Same, но blocked network не доходит до Telemt | Вероятна фильтрация по JA4 + destination/IP/SNI/network до приложения. |
+| Same | Same, доходит и `auth_success>0` | JA4 ClientHello не является точкой отказа; искать post-auth проблему. |
+| Different | Blocked только один JA4 | Вероятен client-version/platform-specific fingerprint block. |
+| Same | `bad_or_probe` растёт, `auth_success=0` | Возможно, доходит не тот клиент/secret или фильтр/прокси ломает поток после ClientHello. |
+
+### 4. Разделить client JA4 и server fingerprint
+
+JA4 ClientHello - это клиентская сторона. Настройки Telemt вроде TLS-front server flight, `mask_host`, ticket-tail или CCS replay не меняют ClientHello, который отправляет Telegram client.
+
+Если фильтр принимает решение строго после ClientHello, то серверные улучшения могут не помочь. В этом случае полезные действия:
+
+- проверить обновление Telegram client;
+- сравнить платформы и версии клиента;
+- проверить, меняется ли JA4 на другой версии;
+- проверить, блокируется ли тот же JA4 к другому destination;
+- проверить, блокируется ли другой JA4 к тому же Telemt IP/SNI;
+- собрать evidence для client-side fingerprint fix.
+
+Если ClientHello проходит, а блокировка возникает после server response, тогда уже важны:
+
+- форма FakeTLS server flight;
+- TLS front profile fidelity;
+- `mask_host` поведение для non-auth clients;
+- certificate/provenance fallback для сканеров;
+- TCP relay behavior;
+- upstream route к Telegram.
+
+### 5. Коррелировать с packet capture
+
+Telemt collector показывает только то, что процесс увидел. Для подтверждения фильтрации до Telemt нужен внешний capture.
+
+На сервере:
+
+```bash
+sudo tcpdump -i any -w telemt-clienthello.pcap host CLIENT_IP and port 443
+```
+
+Быстрый tshark вывод ClientHello fields:
+
+```bash
+tshark -r telemt-clienthello.pcap -Y "tls.handshake.type == 1" -T fields \
+  -e frame.time_epoch \
+  -e ip.src \
+  -e ip.dst \
+  -e tcp.srcport \
+  -e tcp.dstport \
+  -e tls.handshake.extensions_server_name \
+  -e tls.handshake.extensions_alpn_str
+```
+
+Если на клиентской стороне capture видит ClientHello, а серверный capture не видит, проблема в сети между клиентом и сервером. Если серверный capture видит ClientHello, но Telemt API не видит fingerprint, проверьте порт, listener, PROXY protocol, TLS record fragmentation и bounds/errors.
+
+## Практические сценарии
+
+### Сценарий A: один JA4 перестал работать у многих пользователей
+
+Признаки:
+
+- один `ja4` доминирует в жалобах;
+- у разных source CIDR нет `auth_success`;
+- working пользователи используют другой JA4;
+- обновление клиента меняет поведение.
+
+Вероятный вывод: фильтр на стороне сети научился распознавать конкретный ClientHello family.
+
+Действия:
+
+- сравнить Telegram client versions;
+- проверить, не используют ли пользователи старые клиенты;
+- собрать `ja4`, `ja4_raw`, platform/version, source network;
+- проверить тот же client через другую сеть;
+- проверить другой client version через ту же сеть.
+
+### Сценарий B: один CIDR не работает, JA4 обычный
+
+Признаки:
+
+- тот же `ja4` успешно работает из других сетей;
+- проблемный `/24` или `/56` не доходит до Telemt или не получает `auth_success`;
+- нет общей корреляции по версии клиента.
+
+Вероятный вывод: проблема не в JA4 alone, а в source network policy или destination reputation.
+
+Действия:
+
+- сменить route/VPS/IP;
+- проверить port;
+- проверить SNI/domain reputation;
+- сравнить с другим Telemt endpoint;
+- смотреть server-side packet capture.
+
+### Сценарий C: много `bad_or_probe` на одном JA4
+
+Признаки:
+
+- `bad_or_probe` высокий;
+- `by_user` пустой или слабый;
+- source IP/CIDR разнообразные;
+- попытки не соответствуют реальным пользователям.
+
+Вероятный вывод: активное сканирование или нерелевантный TLS traffic с похожим ClientHello.
+
+Действия:
+
+- смотреть `/beobachten` по IP classes;
+- проверить `unknown_tls_sni` и bad-client counters;
+- убедиться, что fallback `mask_host` отвечает правдоподобно;
+- не делать вывод о блокировке пользователей только по global `bad_or_probe`.
+
+### Сценарий D: `auth_success` есть, но пользователь жалуется
+
+Признаки:
+
+- fingerprint присутствует в `by_user`;
+- `auth_success` растёт;
+- соединение проходит TLS-auth.
+
+Вероятный вывод: JA4 ClientHello не является причиной отказа в этом случае.
+
+Действия:
+
+- проверить user enabled/disabled status;
+- проверить quota;
+- проверить direct/ME route;
+- проверить upstream health;
+- проверить runtime events;
+- смотреть relay/session logs.
+
+## Что нельзя вывести из JA3/JA4
+
+JA3/JA4 не говорят:
+
+- почему сеть приняла решение о блокировке;
+- какой именно vendor DPI используется;
+- был ли block только по JA4 или по связке JA4+IP+SNI;
+- что произошло с соединением после TLS-auth;
+- как выглядит server-side TLS fingerprint;
+- как ведёт себя HTTP layer после TLS.
+
+JA3/JA4 также не являются уникальной идентичностью человека. Это fingerprint клиентской TLS-реализации и её настроек. Один fingerprint может быть у большого числа пользователей.
+
+## Ограничения collector'а Telemt
+
+- Считается только TLS ClientHello, который полностью дошёл до Telemt.
+- QUIC/DTLS/HTTP JA4 variants не собираются.
+- Truncated ClientHello не fingerprint'ится.
+- User scope появляется только после успешной TLS-auth.
+- `by_ip` и `by_cidr` отражают source address после нормализации/PROXY protocol path, если он используется.
+- Collector bounded: при большом количестве уникальных buckets возможен рост `dropped_total`.
+- Retention зависит от `general.beobachten_minutes`.
+- Данные runtime in-memory; это snapshot для диагностики, а не долговременное хранилище.
+
+## Рекомендованный workflow расследования
+
+1. Включить `runtime_edge_enabled=true` и разумный `runtime_edge_top_n`, например `100`.
+2. Зафиксировать baseline в период нормальной работы.
+3. Во время жалобы снять API snapshot и `/beobachten`.
+4. Сравнить `by_user`, `by_ip`, `by_cidr`, `by_fingerprint`.
+5. Проверить, появляется ли problematic source в Telemt вообще.
+6. Если не появляется, снять packet capture на сервере и клиенте.
+7. Если появляется без `auth_success`, проверить secret/client/proxy link и bad/probe counters.
+8. Если появляется с `auth_success`, исключить JA4 ClientHello как primary cause и перейти к relay/upstream/runtime диагностике.
+9. Если один JA4 стабильно коррелирует с block, собрать client version/platform evidence.
+10. Проверить, меняет ли обновление клиента JA4 и результат подключения.
+
+## Минимальный incident report
+
+Для полезного отчёта по JA4-based блокировке соберите:
+
+```text
+time_window:
+telemt_version:
+server_ip:
+server_port:
+tls_domain:
+mask_host:
+client_platform:
+client_version:
+source_network:
+source_ip_or_cidr:
+ja4:
+ja4_raw:
+ja3:
+total:
+auth_success:
+bad_or_probe:
+seen_in_by_user: yes/no
+seen_in_by_ip: yes/no
+seen_in_by_cidr: yes/no
+server_tcpdump_seen_clienthello: yes/no
+client_tcpdump_sent_clienthello: yes/no
+works_from_other_network: yes/no
+works_with_other_client_version: yes/no
+```
+
+Этот набор обычно достаточен, чтобы отличить client fingerprint block от IP/SNI/reputation block и от post-auth проблем Telemt.
+
+## Источники форматов
+
+- JA3 reference: https://github.com/salesforce/ja3
+- JA4 technical details: https://github.com/FoxIO-LLC/ja4/blob/main/technical_details/JA4.md
+

docs/Config_params/CONFIG_PARAMS.en.md

@@ -85,145 +85,7 @@ This document lists all configuration keys accepted by `config.toml`.
 
 # [general]
 
-| Key | Type | Default |
-| --- | ---- | ------- |
-| [`data_path`](#data_path) | `String` | — |
-| [`prefer_ipv6`](#prefer_ipv6) | `bool` | `false` |
-| [`fast_mode`](#fast_mode) | `bool` | `true` |
-| [`use_middle_proxy`](#use_middle_proxy) | `bool` | `true` |
-| [`proxy_secret_path`](#proxy_secret_path) | `String` | `"proxy-secret"` |
-| [`proxy_config_v4_cache_path`](#proxy_config_v4_cache_path) | `String` | `"cache/proxy-config-v4.txt"` |
-| [`proxy_config_v6_cache_path`](#proxy_config_v6_cache_path) | `String` | `"cache/proxy-config-v6.txt"` |
-| [`ad_tag`](#ad_tag) | `String` | — |
-| [`middle_proxy_nat_ip`](#middle_proxy_nat_ip) | `IpAddr` | — |
-| [`middle_proxy_nat_probe`](#middle_proxy_nat_probe) | `bool` | `true` |
-| [`middle_proxy_nat_stun`](#middle_proxy_nat_stun) | `String` | — |
-| [`middle_proxy_nat_stun_servers`](#middle_proxy_nat_stun_servers) | `String[]` | `[]` |
-| [`stun_nat_probe_concurrency`](#stun_nat_probe_concurrency) | `usize` | `8` |
-| [`middle_proxy_pool_size`](#middle_proxy_pool_size) | `usize` | `8` |
-| [`middle_proxy_warm_standby`](#middle_proxy_warm_standby) | `usize` | `16` |
-| [`me_init_retry_attempts`](#me_init_retry_attempts) | `u32` | `0` |
-| [`me2dc_fallback`](#me2dc_fallback) | `bool` | `true` |
-| [`me2dc_fast`](#me2dc_fast) | `bool` | `true` |
-| [`me_keepalive_enabled`](#me_keepalive_enabled) | `bool` | `true` |
-| [`me_keepalive_interval_secs`](#me_keepalive_interval_secs) | `u64` | `8` |
-| [`me_keepalive_jitter_secs`](#me_keepalive_jitter_secs) | `u64` | `2` |
-| [`me_keepalive_payload_random`](#me_keepalive_payload_random) | `bool` | `true` |
-| [`rpc_proxy_req_every`](#rpc_proxy_req_every) | `u64` | `0` |
-| [`me_writer_cmd_channel_capacity`](#me_writer_cmd_channel_capacity) | `usize` | `4096` |
-| [`me_route_channel_capacity`](#me_route_channel_capacity) | `usize` | `768` |
-| [`me_c2me_channel_capacity`](#me_c2me_channel_capacity) | `usize` | `1024` |
-| [`me_c2me_send_timeout_ms`](#me_c2me_send_timeout_ms) | `u64` | `4000` |
-| [`me_reader_route_data_wait_ms`](#me_reader_route_data_wait_ms) | `u64` | `2` |
-| [`me_d2c_flush_batch_max_frames`](#me_d2c_flush_batch_max_frames) | `usize` | `32` |
-| [`me_d2c_flush_batch_max_bytes`](#me_d2c_flush_batch_max_bytes) | `usize` | `131072` |
-| [`me_d2c_flush_batch_max_delay_us`](#me_d2c_flush_batch_max_delay_us) | `u64` | `500` |
-| [`me_d2c_ack_flush_immediate`](#me_d2c_ack_flush_immediate) | `bool` | `true` |
-| [`me_quota_soft_overshoot_bytes`](#me_quota_soft_overshoot_bytes) | `u64` | `65536` |
-| [`me_d2c_frame_buf_shrink_threshold_bytes`](#me_d2c_frame_buf_shrink_threshold_bytes) | `usize` | `262144` |
-| [`direct_relay_copy_buf_c2s_bytes`](#direct_relay_copy_buf_c2s_bytes) | `usize` | `65536` |
-| [`direct_relay_copy_buf_s2c_bytes`](#direct_relay_copy_buf_s2c_bytes) | `usize` | `262144` |
-| [`crypto_pending_buffer`](#crypto_pending_buffer) | `usize` | `262144` |
-| [`max_client_frame`](#max_client_frame) | `usize` | `16777216` |
-| [`desync_all_full`](#desync_all_full) | `bool` | `false` |
-| [`beobachten`](#beobachten) | `bool` | `true` |
-| [`beobachten_minutes`](#beobachten_minutes) | `u64` | `10` |
-| [`beobachten_flush_secs`](#beobachten_flush_secs) | `u64` | `15` |
-| [`beobachten_file`](#beobachten_file) | `String` | `"cache/beobachten.txt"` |
-| [`hardswap`](#hardswap) | `bool` | `true` |
-| [`me_warmup_stagger_enabled`](#me_warmup_stagger_enabled) | `bool` | `true` |
-| [`me_warmup_step_delay_ms`](#me_warmup_step_delay_ms) | `u64` | `500` |
-| [`me_warmup_step_jitter_ms`](#me_warmup_step_jitter_ms) | `u64` | `300` |
-| [`me_reconnect_max_concurrent_per_dc`](#me_reconnect_max_concurrent_per_dc) | `u32` | `8` |
-| [`me_reconnect_backoff_base_ms`](#me_reconnect_backoff_base_ms) | `u64` | `500` |
-| [`me_reconnect_backoff_cap_ms`](#me_reconnect_backoff_cap_ms) | `u64` | `30000` |
-| [`me_reconnect_fast_retry_count`](#me_reconnect_fast_retry_count) | `u32` | `16` |
-| [`me_single_endpoint_shadow_writers`](#me_single_endpoint_shadow_writers) | `u8` | `2` |
-| [`me_single_endpoint_outage_mode_enabled`](#me_single_endpoint_outage_mode_enabled) | `bool` | `true` |
-| [`me_single_endpoint_outage_disable_quarantine`](#me_single_endpoint_outage_disable_quarantine) | `bool` | `true` |
-| [`me_single_endpoint_outage_backoff_min_ms`](#me_single_endpoint_outage_backoff_min_ms) | `u64` | `250` |
-| [`me_single_endpoint_outage_backoff_max_ms`](#me_single_endpoint_outage_backoff_max_ms) | `u64` | `3000` |
-| [`me_single_endpoint_shadow_rotate_every_secs`](#me_single_endpoint_shadow_rotate_every_secs) | `u64` | `900` |
-| [`me_floor_mode`](#me_floor_mode) | `"static"` or `"adaptive"` | `"adaptive"` |
-| [`me_adaptive_floor_idle_secs`](#me_adaptive_floor_idle_secs) | `u64` | `90` |
-| [`me_adaptive_floor_min_writers_single_endpoint`](#me_adaptive_floor_min_writers_single_endpoint) | `u8` | `1` |
-| [`me_adaptive_floor_min_writers_multi_endpoint`](#me_adaptive_floor_min_writers_multi_endpoint) | `u8` | `1` |
-| [`me_adaptive_floor_recover_grace_secs`](#me_adaptive_floor_recover_grace_secs) | `u64` | `180` |
-| [`me_adaptive_floor_writers_per_core_total`](#me_adaptive_floor_writers_per_core_total) | `u16` | `48` |
-| [`me_adaptive_floor_cpu_cores_override`](#me_adaptive_floor_cpu_cores_override) | `u16` | `0` |
-| [`me_adaptive_floor_max_extra_writers_single_per_core`](#me_adaptive_floor_max_extra_writers_single_per_core) | `u16` | `1` |
-| [`me_adaptive_floor_max_extra_writers_multi_per_core`](#me_adaptive_floor_max_extra_writers_multi_per_core) | `u16` | `2` |
-| [`me_adaptive_floor_max_active_writers_per_core`](#me_adaptive_floor_max_active_writers_per_core) | `u16` | `64` |
-| [`me_adaptive_floor_max_warm_writers_per_core`](#me_adaptive_floor_max_warm_writers_per_core) | `u16` | `64` |
-| [`me_adaptive_floor_max_active_writers_global`](#me_adaptive_floor_max_active_writers_global) | `u32` | `256` |
-| [`me_adaptive_floor_max_warm_writers_global`](#me_adaptive_floor_max_warm_writers_global) | `u32` | `256` |
-| [`upstream_connect_retry_attempts`](#upstream_connect_retry_attempts) | `u32` | `2` |
-| [`upstream_connect_retry_backoff_ms`](#upstream_connect_retry_backoff_ms) | `u64` | `100` |
-| [`upstream_connect_budget_ms`](#upstream_connect_budget_ms) | `u64` | `3000` |
-| [`upstream_unhealthy_fail_threshold`](#upstream_unhealthy_fail_threshold) | `u32` | `5` |
-| [`upstream_connect_failfast_hard_errors`](#upstream_connect_failfast_hard_errors) | `bool` | `false` |
-| [`stun_iface_mismatch_ignore`](#stun_iface_mismatch_ignore) | `bool` | `false` |
-| [`unknown_dc_log_path`](#unknown_dc_log_path) | `String` | `"unknown-dc.txt"` |
-| [`unknown_dc_file_log_enabled`](#unknown_dc_file_log_enabled) | `bool` | `false` |
-| [`log_level`](#log_level) | `"debug"`, `"verbose"`, `"normal"`, or `"silent"` | `"normal"` |
-| [`disable_colors`](#disable_colors) | `bool` | `false` |
-| [`me_socks_kdf_policy`](#me_socks_kdf_policy) | `"strict"` or `"compat"` | `"strict"` |
-| [`me_route_backpressure_enabled`](#me_route_backpressure_enabled) | `bool` | `false` |
-| [`me_route_fairshare_enabled`](#me_route_fairshare_enabled) | `bool` | `false` |
-| [`me_route_backpressure_base_timeout_ms`](#me_route_backpressure_base_timeout_ms) | `u64` | `25` |
-| [`me_route_backpressure_high_timeout_ms`](#me_route_backpressure_high_timeout_ms) | `u64` | `120` |
-| [`me_route_backpressure_high_watermark_pct`](#me_route_backpressure_high_watermark_pct) | `u8` | `80` |
-| [`me_health_interval_ms_unhealthy`](#me_health_interval_ms_unhealthy) | `u64` | `1000` |
-| [`me_health_interval_ms_healthy`](#me_health_interval_ms_healthy) | `u64` | `3000` |
-| [`me_admission_poll_ms`](#me_admission_poll_ms) | `u64` | `1000` |
-| [`me_warn_rate_limit_ms`](#me_warn_rate_limit_ms) | `u64` | `5000` |
-| [`me_route_no_writer_mode`](#me_route_no_writer_mode) | `"async_recovery_failfast"`, `"inline_recovery_legacy"`, or `"hybrid_async_persistent"` | `"hybrid_async_persistent"` |
-| [`me_route_no_writer_wait_ms`](#me_route_no_writer_wait_ms) | `u64` | `250` |
-| [`me_route_hybrid_max_wait_ms`](#me_route_hybrid_max_wait_ms) | `u64` | `3000` |
-| [`me_route_blocking_send_timeout_ms`](#me_route_blocking_send_timeout_ms) | `u64` | `250` |
-| [`me_route_inline_recovery_attempts`](#me_route_inline_recovery_attempts) | `u32` | `3` |
-| [`me_route_inline_recovery_wait_ms`](#me_route_inline_recovery_wait_ms) | `u64` | `3000` |
-| [`fast_mode_min_tls_record`](#fast_mode_min_tls_record) | `usize` | `0` |
-| [`update_every`](#update_every) | `u64` | `300` |
-| [`me_reinit_every_secs`](#me_reinit_every_secs) | `u64` | `900` |
-| [`me_hardswap_warmup_delay_min_ms`](#me_hardswap_warmup_delay_min_ms) | `u64` | `1000` |
-| [`me_hardswap_warmup_delay_max_ms`](#me_hardswap_warmup_delay_max_ms) | `u64` | `2000` |
-| [`me_hardswap_warmup_extra_passes`](#me_hardswap_warmup_extra_passes) | `u8` | `3` |
-| [`me_hardswap_warmup_pass_backoff_base_ms`](#me_hardswap_warmup_pass_backoff_base_ms) | `u64` | `500` |
-| [`me_config_stable_snapshots`](#me_config_stable_snapshots) | `u8` | `2` |
-| [`me_config_apply_cooldown_secs`](#me_config_apply_cooldown_secs) | `u64` | `300` |
-| [`me_snapshot_require_http_2xx`](#me_snapshot_require_http_2xx) | `bool` | `true` |
-| [`me_snapshot_reject_empty_map`](#me_snapshot_reject_empty_map) | `bool` | `true` |
-| [`me_snapshot_min_proxy_for_lines`](#me_snapshot_min_proxy_for_lines) | `u32` | `1` |
-| [`proxy_secret_stable_snapshots`](#proxy_secret_stable_snapshots) | `u8` | `2` |
-| [`proxy_secret_rotate_runtime`](#proxy_secret_rotate_runtime) | `bool` | `true` |
-| [`me_secret_atomic_snapshot`](#me_secret_atomic_snapshot) | `bool` | `true` |
-| [`proxy_secret_len_max`](#proxy_secret_len_max) | `usize` | `256` |
-| [`me_pool_drain_ttl_secs`](#me_pool_drain_ttl_secs) | `u64` | `90` |
-| [`me_instadrain`](#me_instadrain) | `bool` | `false` |
-| [`me_pool_drain_threshold`](#me_pool_drain_threshold) | `u64` | `32` |
-| [`me_pool_drain_soft_evict_enabled`](#me_pool_drain_soft_evict_enabled) | `bool` | `true` |
-| [`me_pool_drain_soft_evict_grace_secs`](#me_pool_drain_soft_evict_grace_secs) | `u64` | `10` |
-| [`me_pool_drain_soft_evict_per_writer`](#me_pool_drain_soft_evict_per_writer) | `u8` | `2` |
-| [`me_pool_drain_soft_evict_budget_per_core`](#me_pool_drain_soft_evict_budget_per_core) | `u16` | `16` |
-| [`me_pool_drain_soft_evict_cooldown_ms`](#me_pool_drain_soft_evict_cooldown_ms) | `u64` | `1000` |
-| [`me_bind_stale_mode`](#me_bind_stale_mode) | `"never"`, `"ttl"`, or `"always"` | `"ttl"` |
-| [`me_bind_stale_ttl_secs`](#me_bind_stale_ttl_secs) | `u64` | `90` |
-| [`me_pool_min_fresh_ratio`](#me_pool_min_fresh_ratio) | `f32` | `0.8` |
-| [`me_reinit_drain_timeout_secs`](#me_reinit_drain_timeout_secs) | `u64` | `90` |
-| [`proxy_secret_auto_reload_secs`](#proxy_secret_auto_reload_secs) | `u64` | `3600` |
-| [`proxy_config_auto_reload_secs`](#proxy_config_auto_reload_secs) | `u64` | `3600` |
-| [`me_reinit_singleflight`](#me_reinit_singleflight) | `bool` | `true` |
-| [`me_reinit_trigger_channel`](#me_reinit_trigger_channel) | `usize` | `64` |
-| [`me_reinit_coalesce_window_ms`](#me_reinit_coalesce_window_ms) | `u64` | `200` |
-| [`me_deterministic_writer_sort`](#me_deterministic_writer_sort) | `bool` | `true` |
-| [`me_writer_pick_mode`](#me_writer_pick_mode) | `"sorted_rr"` or `"p2c"` | `"p2c"` |
-| [`me_writer_pick_sample_size`](#me_writer_pick_sample_size) | `u8` | `3` |
-| [`ntp_check`](#ntp_check) | `bool` | `true` |
-| [`ntp_servers`](#ntp_servers) | `String[]` | `["pool.ntp.org"]` |
-| [`auto_degradation_enabled`](#auto_degradation_enabled) | `bool` | `true` |
-| [`degradation_min_unavailable_dc_groups`](#degradation_min_unavailable_dc_groups) | `u8` | `2` |
-| [`rst_on_close`](#rst_on_close) | `"off"`, `"errors"`, or `"always"` | `"off"` |
+
 | Key | Type | Default | Hot-Reload |
 | --- | ---- | ------- | ---------- |
 | [`data_path`](#data_path) | `String` | — | `✘` |
@@ -770,7 +632,7 @@ This document lists all configuration keys accepted by `config.toml`.
     ```
 ## beobachten
   - **Constraints / validation**: `bool`.
-  - **Description**: Enables per-IP forensic observation buckets.
+  - **Description**: Enables per-IP forensic observation buckets and appends TLS JA3/JA4 fingerprint snapshots to Beobachten output when available.
   - **Example**:
 
     ```toml
@@ -779,7 +641,7 @@ This document lists all configuration keys accepted by `config.toml`.
     ```
 ## beobachten_minutes
   - **Constraints / validation**: Must be `> 0` (minutes).
-  - **Description**: Retention window (minutes) for per-IP observation buckets.
+  - **Description**: Retention window (minutes) for per-IP observation buckets and in-memory TLS fingerprint buckets.
   - **Example**:
 
     ```toml
@@ -1943,6 +1805,7 @@ This document lists all configuration keys accepted by `config.toml`.
 | [`listen_unix_sock`](#listen_unix_sock) | `String` | — | `✘` |
 | [`listen_unix_sock_perm`](#listen_unix_sock_perm) | `String` | — | `✘` |
 | [`listen_tcp`](#listen_tcp) | `bool` | — (auto) | `✘` |
+| [`client_mss`](#client_mss) | `String` | `""` | `✘` |
 | [`proxy_protocol`](#proxy_protocol) | `bool` | `false` | `✘` |
 | [`proxy_protocol_header_timeout_ms`](#proxy_protocol_header_timeout_ms) | `u64` | `500` | `✘` |
 | [`proxy_protocol_trusted_cidrs`](#proxy_protocol_trusted_cidrs) | `IpNetwork[]` | `[]` | `✘` |
@@ -2025,6 +1888,16 @@ This document lists all configuration keys accepted by `config.toml`.
     listen_unix_sock = "/run/telemt.sock"
     listen_tcp = true
     ```
+## client_mss
+  - **Constraints / validation**: `String`. Empty or omitted means do not change kernel MSS. Presets: `"extreme-low"` = `88`, `"tspu"` = `92`, `"2in8"` = `256`. Custom decimal strings must be within `88..=4096`.
+  - **Description**: Client-facing TCP MSS applied to TCP listener sockets before `listen(2)`, so Linux can announce it in SYN/ACK. This affects only proxy client TCP listeners, not API, metrics, Unix sockets, Telegram upstreams, ME sockets, or mask backend connections. Changes require listener restart/rebind.
+  - **Performance note**: Low MSS increases packet count predictably. Approximate segment multiplier is `ceil(1460 / client_mss)`.
+  - **Example**:
+
+    ```toml
+    [server]
+    client_mss = "tspu"
+    ```
 ## proxy_protocol
   - **Constraints / validation**: `bool`.
   - **Description**: Enables HAProxy PROXY protocol parsing on incoming connections (PROXY v1/v2). When enabled, client source address is taken from the PROXY header.
@@ -2311,7 +2184,7 @@ Note: This section also accepts the legacy alias `[server.admin_api]` (same sche
     ```
 ## runtime_edge_top_n
   - **Constraints / validation**: `1..=1000`.
-  - **Description**: Top-N size for edge connection leaderboard.
+  - **Description**: Top-N size for edge connection and TLS fingerprint leaderboard snapshots.
   - **Example**:
 
     ```toml
@@ -2345,6 +2218,11 @@ Note: This section also accepts the legacy alias `[server.admin_api]` (same sche
 | --- | ---- | ------- | ---------- |
 | [`ip`](#ip) | `IpAddr` | — | `✘` |
 | [`port`](#port-serverlisteners) | `u16` | `server.port` | `✘` |
+| [`client_mss`](#client_mss-serverlisteners) | `String` | `[server].client_mss` | `✘` |
+| [`synlimit`](#synlimit-serverlisteners) | `false`, `"iptables"`, or `"nftables"` | `false` | `✔` |
+| [`synlimit_seconds`](#synlimit_seconds-serverlisteners) | `u32` | `1` | `✔` |
+| [`synlimit_hitcount`](#synlimit_hitcount-serverlisteners) | `u32` | `1` | `✔` |
+| [`synlimit_burst`](#synlimit_burst-serverlisteners) | `u32` | `2` | `✔` |
 | [`announce`](#announce) | `String` | — | `✘` |
 | [`announce_ip`](#announce_ip) | `IpAddr` | — | `✘` |
 | [`proxy_protocol`](#proxy_protocol) | `bool` | — | `✘` |
@@ -2369,6 +2247,69 @@ Note: This section also accepts the legacy alias `[server.admin_api]` (same sche
     ip = "0.0.0.0"
     port = 443
     ```
+## client_mss (server.listeners)
+  - **Constraints / validation**: `String` (optional). Same values as `[server].client_mss`.
+  - **Description**: Per-listener MSS override. When omitted, inherits `[server].client_mss`; when set to an empty string, disables MSS shaping for this listener even if the global value is set. Changes require listener restart/rebind.
+  - **Example**:
+
+    ```toml
+    [[server.listeners]]
+    ip = "0.0.0.0"
+    port = 443
+    client_mss = "256"
+    ```
+## synlimit (server.listeners)
+  - **Constraints / validation**: `false`, `"iptables"`, or `"nftables"`. Omitted or `false` disables SYN limiting for this listener.
+  - **Description**: Installs per-listener Linux netfilter SYN limiter rules for the listener port. `"iptables"` uses `iptables`/`ip6tables` filter rules with the `hashlimit` match as a per-source token bucket. `"nftables"` uses per-source `meter` rules with `limit rate over` and auto-detects whether the host already uses `inet`, `ip`, or `ip6` table families before creating Telemt-owned tables. The token-bucket rate is `synlimit_hitcount / synlimit_seconds`; `synlimit_burst` controls the burst size. Rules are reconciled at runtime and removed during graceful Telemt shutdown; `SIGKILL` cannot be cleaned up by the process. Requires CAP_NET_ADMIN. `synlimit*` changes hot-reload for existing listener endpoints; changing listener `ip` or `port` still requires restart/rebind.
+  - **Example**:
+
+    ```toml
+    [[server.listeners]]
+    ip = "0.0.0.0"
+    port = 443
+    synlimit = "iptables"
+
+    [[server.listeners]]
+    ip = "::"
+    port = 443
+    synlimit = "nftables"
+    ```
+## synlimit_seconds (server.listeners)
+  - **Constraints / validation**: `u32`, must be `> 0`. Default is `1`.
+  - **Description**: Token-bucket interval for both SYN limiter backends. The rate is `synlimit_hitcount / synlimit_seconds` and is rendered to native netfilter rate units (`second`, `minute`, `hour`, or `day`).
+  - **Example**:
+
+    ```toml
+    [[server.listeners]]
+    ip = "0.0.0.0"
+    port = 443
+    synlimit = "iptables"
+    synlimit_seconds = 1
+    ```
+## synlimit_hitcount (server.listeners)
+  - **Constraints / validation**: `u32`, must be `> 0`. Default is `1`.
+  - **Description**: Token-bucket rate amount for both SYN limiter backends. Together with `synlimit_seconds`, it defines the allowed source-IP SYN rate before excess SYN packets are dropped.
+  - **Example**:
+
+    ```toml
+    [[server.listeners]]
+    ip = "0.0.0.0"
+    port = 443
+    synlimit = "iptables"
+    synlimit_hitcount = 1
+    ```
+## synlimit_burst (server.listeners)
+  - **Constraints / validation**: `u32`, must be `> 0`. Default is `2`.
+  - **Description**: Token-bucket burst size for both SYN limiter backends. Higher values allow short connection bursts from the same source IP before the steady-state `synlimit_hitcount / synlimit_seconds` rate is enforced.
+  - **Example**:
+
+    ```toml
+    [[server.listeners]]
+    ip = "0.0.0.0"
+    port = 443
+    synlimit = "iptables"
+    synlimit_burst = 2
+    ```
 ## announce
   - **Constraints / validation**: `String` (optional). Must not be empty when set.
   - **Description**: Public IP/domain announced in proxy links for this listener. Takes precedence over `announce_ip`.
@@ -2525,41 +2466,6 @@ Note: This section also accepts the legacy alias `[server.admin_api]` (same sche
 # [censorship]
 
 
-| Key | Type | Default |
-| --- | ---- | ------- |
-| [`tls_domain`](#tls_domain) | `String` | `"petrovich.ru"` |
-| [`tls_domains`](#tls_domains) | `String[]` | `[]` |
-| [`unknown_sni_action`](#unknown_sni_action) | `"drop"`, `"mask"`, `"accept"`, `"reject_handshake"` | `"drop"` |
-| [`tls_fetch_scope`](#tls_fetch_scope) | `String` | `""` |
-| [`tls_fetch`](#tls_fetch) | `Table` | built-in defaults |
-| [`mask`](#mask) | `bool` | `true` |
-| [`mask_host`](#mask_host) | `String` | — |
-| [`mask_port`](#mask_port) | `u16` | `443` |
-| [`exclusive_mask`](#exclusive_mask) | `Map<String,String>` | `{}` |
-| [`mask_unix_sock`](#mask_unix_sock) | `String` | — |
-| [`fake_cert_len`](#fake_cert_len) | `usize` | `2048` |
-| [`tls_emulation`](#tls_emulation) | `bool` | `true` |
-| [`tls_front_dir`](#tls_front_dir) | `String` | `"tlsfront"` |
-| [`server_hello_delay_min_ms`](#server_hello_delay_min_ms) | `u64` | `0` |
-| [`server_hello_delay_max_ms`](#server_hello_delay_max_ms) | `u64` | `0` |
-| [`tls_new_session_tickets`](#tls_new_session_tickets) | `u8` | `0` |
-| [`tls_full_cert_ttl_secs`](#tls_full_cert_ttl_secs) | `u64` | `90` |
-| [`serverhello_compact`](#serverhello_compact) | `bool` | `false` |
-| [`alpn_enforce`](#alpn_enforce) | `bool` | `true` |
-| [`mask_proxy_protocol`](#mask_proxy_protocol) | `u8` | `0` |
-| [`mask_shape_hardening`](#mask_shape_hardening) | `bool` | `true` |
-| [`mask_shape_hardening_aggressive_mode`](#mask_shape_hardening_aggressive_mode) | `bool` | `false` |
-| [`mask_shape_bucket_floor_bytes`](#mask_shape_bucket_floor_bytes) | `usize` | `512` |
-| [`mask_shape_bucket_cap_bytes`](#mask_shape_bucket_cap_bytes) | `usize` | `4096` |
-| [`mask_shape_above_cap_blur`](#mask_shape_above_cap_blur) | `bool` | `false` |
-| [`mask_shape_above_cap_blur_max_bytes`](#mask_shape_above_cap_blur_max_bytes) | `usize` | `512` |
-| [`mask_relay_max_bytes`](#mask_relay_max_bytes) | `usize` | `5242880` |
-| [`mask_relay_timeout_ms`](#mask_relay_timeout_ms) | `u64` | `60_000` |
-| [`mask_relay_idle_timeout_ms`](#mask_relay_idle_timeout_ms) | `u64` | `5_000` |
-| [`mask_classifier_prefetch_timeout_ms`](#mask_classifier_prefetch_timeout_ms) | `u64` | `5` |
-| [`mask_timing_normalization_enabled`](#mask_timing_normalization_enabled) | `bool` | `false` |
-| [`mask_timing_normalization_floor_ms`](#mask_timing_normalization_floor_ms) | `u64` | `0` |
-| [`mask_timing_normalization_ceiling_ms`](#mask_timing_normalization_ceiling_ms) | `u64` | `0` |
 | Key | Type | Default | Hot-Reload |
 | --- | ---- | ------- | ---------- |
 | [`tls_domain`](#tls_domain) | `String` | `"petrovich.ru"` | `✘` |
@@ -3107,6 +3013,7 @@ If your backend or network is very bandwidth-constrained, reduce cap first. If p
 | Key | Type | Default | Hot-Reload |
 | --- | ---- | ------- | ---------- |
 | [`users`](#users) | `Map<String, String>` | `{"default": "000…000"}` | `✔` |
+| [`user_enabled`](#user_enabled-1) | `Map<String, bool>` | `{}` | `✔` |
 | [`user_ad_tags`](#user_ad_tags) | `Map<String, String>` | `{}` | `✔` |
 | [`user_max_tcp_conns`](#user_max_tcp_conns) | `Map<String, usize>` | `{}` | `✔` |
 | [`user_max_tcp_conns_global_each`](#user_max_tcp_conns_global_each) | `usize` | `0` | `✔` |
@@ -3133,6 +3040,16 @@ If your backend or network is very bandwidth-constrained, reduce cap first. If p
     alice = "00112233445566778899aabbccddeeff"
     bob   = "0123456789abcdef0123456789abcdef"
     ```
+## user_enabled
+  - **Constraints / validation**: `Map<String, bool>`.
+  - **Description**: Optional per-user enable overrides. Missing users are enabled by default. A value of `false` disables new sessions for that user; setting the value to `true` is accepted but equivalent to removing the override. API enable operations remove the override, while disable operations write `false`.
+  - **Runtime behavior**: Hot reload applies this map immediately. Users disabled through API or config reload are rejected after successful authentication and active runtime sessions for that username are cancelled.
+  - **Example**:
+
+    ```toml
+    [access.user_enabled]
+    alice = false
+    ```
 ## user_ad_tags
   - **Constraints / validation**: Each value must be **exactly 32 hex characters** (same format as `general.ad_tag`). An all-zero tag is allowed but logs a warning.
   - **Description**: Per-user sponsored-channel ad tag override. When a user has an entry here, it takes precedence over `general.ad_tag`.
@@ -3266,7 +3183,7 @@ If your backend or network is very bandwidth-constrained, reduce cap first. If p
 
 ## user_rate_limits
   - **Constraints / validation**: Table `username -> { up_bps, down_bps }`. At least one direction must be non-zero.
-  - **Description**: Per-user bandwidth caps in bytes/sec for upload (`up_bps`) and download (`down_bps`).
+  - **Description**: Per-user bandwidth caps in bits/sec for upload (`up_bps`) and download (`down_bps`).
   - **Example**:
 
     ```toml
@@ -3293,6 +3210,7 @@ If your backend or network is very bandwidth-constrained, reduce cap first. If p
 | [`scopes`](#scopes) | `String` | `""` | `✘` |
 | [`ipv4`](#ipv4-upstreams) | `bool` | — (auto) | `✘` |
 | [`ipv6`](#ipv6-upstreams) | `bool` | — (auto) | `✘` |
+| [`prefer`](#prefer-upstreams) | `4` or `6` | effective `[network].prefer` | `✘` |
 | [`interface`](#interface) | `String` | — | `✘` |
 | [`bind_addresses`](#bind_addresses) | `String[]` | — | `✘` |
 | [`bindtodevice`](#bindtodevice) | `String` | — | `✘` |
@@ -3364,7 +3282,7 @@ If your backend or network is very bandwidth-constrained, reduce cap first. If p
     ```
 ## ipv6 (upstreams)
   - **Constraints / validation**: `bool` (optional).
-  - **Description**: Allows IPv6 DC targets for this upstream. When omitted, Telemt auto-detects support from runtime connectivity state.
+  - **Description**: Allows IPv6 DC targets for this upstream. When omitted, Telemt auto-detects support from runtime connectivity state. Set this to `true` when the upstream proxy is reachable from the local host over IPv4 but the proxy itself can connect to Telegram DCs over IPv6.
   - **Example**:
 
     ```toml
@@ -3372,6 +3290,18 @@ If your backend or network is very bandwidth-constrained, reduce cap first. If p
     type = "direct"
     ipv6 = false
     ```
+## prefer (upstreams)
+  - **Constraints / validation**: Optional integer. Must be `4` or `6`.
+  - **Description**: Overrides the IP family preference for Telegram DC targets selected through this upstream. When omitted, the upstream inherits the effective global `[network].prefer` decision. Use `prefer = 6` together with `ipv6 = true` for a SOCKS or Shadowsocks upstream that can egress over IPv6 even when the local Telemt host is IPv4-only.
+  - **Example**:
+
+    ```toml
+    [[upstreams]]
+    type = "socks5"
+    address = "192.0.2.10:1080"
+    ipv6 = true
+    prefer = 6
+    ```
 ## interface
   - **Constraints / validation**: `String` (optional).
     - For `"direct"`: may be an IP address (used as explicit local bind) or an OS interface name (resolved to an IP at runtime; Unix only).

docs/Config_params/CONFIG_PARAMS.ru.md

@@ -85,145 +85,7 @@
 
 # [general]
 
-| Ключ | Тип | По умолчанию |
-| --- | ---- | ------- |
-| [`data_path`](#data_path) | `String` | — |
-| [`prefer_ipv6`](#prefer_ipv6) | `bool` | `false` |
-| [`fast_mode`](#fast_mode) | `bool` | `true` |
-| [`use_middle_proxy`](#use_middle_proxy) | `bool` | `true` |
-| [`proxy_secret_path`](#proxy_secret_path) | `String` | `"proxy-secret"` |
-| [`proxy_config_v4_cache_path`](#proxy_config_v4_cache_path) | `String` | `"cache/proxy-config-v4.txt"` |
-| [`proxy_config_v6_cache_path`](#proxy_config_v6_cache_path) | `String` | `"cache/proxy-config-v6.txt"` |
-| [`ad_tag`](#ad_tag) | `String` | — |
-| [`middle_proxy_nat_ip`](#middle_proxy_nat_ip) | `IpAddr` | — |
-| [`middle_proxy_nat_probe`](#middle_proxy_nat_probe) | `bool` | `true` |
-| [`middle_proxy_nat_stun`](#middle_proxy_nat_stun) | `String` | — |
-| [`middle_proxy_nat_stun_servers`](#middle_proxy_nat_stun_servers) | `String[]` | `[]` |
-| [`stun_nat_probe_concurrency`](#stun_nat_probe_concurrency) | `usize` | `8` |
-| [`middle_proxy_pool_size`](#middle_proxy_pool_size) | `usize` | `8` |
-| [`middle_proxy_warm_standby`](#middle_proxy_warm_standby) | `usize` | `16` |
-| [`me_init_retry_attempts`](#me_init_retry_attempts) | `u32` | `0` |
-| [`me2dc_fallback`](#me2dc_fallback) | `bool` | `true` |
-| [`me2dc_fast`](#me2dc_fast) | `bool` | `true` |
-| [`me_keepalive_enabled`](#me_keepalive_enabled) | `bool` | `true` |
-| [`me_keepalive_interval_secs`](#me_keepalive_interval_secs) | `u64` | `8` |
-| [`me_keepalive_jitter_secs`](#me_keepalive_jitter_secs) | `u64` | `2` |
-| [`me_keepalive_payload_random`](#me_keepalive_payload_random) | `bool` | `true` |
-| [`rpc_proxy_req_every`](#rpc_proxy_req_every) | `u64` | `0` |
-| [`me_writer_cmd_channel_capacity`](#me_writer_cmd_channel_capacity) | `usize` | `4096` |
-| [`me_route_channel_capacity`](#me_route_channel_capacity) | `usize` | `768` |
-| [`me_c2me_channel_capacity`](#me_c2me_channel_capacity) | `usize` | `1024` |
-| [`me_c2me_send_timeout_ms`](#me_c2me_send_timeout_ms) | `u64` | `4000` |
-| [`me_reader_route_data_wait_ms`](#me_reader_route_data_wait_ms) | `u64` | `2` |
-| [`me_d2c_flush_batch_max_frames`](#me_d2c_flush_batch_max_frames) | `usize` | `32` |
-| [`me_d2c_flush_batch_max_bytes`](#me_d2c_flush_batch_max_bytes) | `usize` | `131072` |
-| [`me_d2c_flush_batch_max_delay_us`](#me_d2c_flush_batch_max_delay_us) | `u64` | `500` |
-| [`me_d2c_ack_flush_immediate`](#me_d2c_ack_flush_immediate) | `bool` | `true` |
-| [`me_quota_soft_overshoot_bytes`](#me_quota_soft_overshoot_bytes) | `u64` | `65536` |
-| [`me_d2c_frame_buf_shrink_threshold_bytes`](#me_d2c_frame_buf_shrink_threshold_bytes) | `usize` | `262144` |
-| [`direct_relay_copy_buf_c2s_bytes`](#direct_relay_copy_buf_c2s_bytes) | `usize` | `65536` |
-| [`direct_relay_copy_buf_s2c_bytes`](#direct_relay_copy_buf_s2c_bytes) | `usize` | `262144` |
-| [`crypto_pending_buffer`](#crypto_pending_buffer) | `usize` | `262144` |
-| [`max_client_frame`](#max_client_frame) | `usize` | `16777216` |
-| [`desync_all_full`](#desync_all_full) | `bool` | `false` |
-| [`beobachten`](#beobachten) | `bool` | `true` |
-| [`beobachten_minutes`](#beobachten_minutes) | `u64` | `10` |
-| [`beobachten_flush_secs`](#beobachten_flush_secs) | `u64` | `15` |
-| [`beobachten_file`](#beobachten_file) | `String` | `"cache/beobachten.txt"` |
-| [`hardswap`](#hardswap) | `bool` | `true` |
-| [`me_warmup_stagger_enabled`](#me_warmup_stagger_enabled) | `bool` | `true` |
-| [`me_warmup_step_delay_ms`](#me_warmup_step_delay_ms) | `u64` | `500` |
-| [`me_warmup_step_jitter_ms`](#me_warmup_step_jitter_ms) | `u64` | `300` |
-| [`me_reconnect_max_concurrent_per_dc`](#me_reconnect_max_concurrent_per_dc) | `u32` | `8` |
-| [`me_reconnect_backoff_base_ms`](#me_reconnect_backoff_base_ms) | `u64` | `500` |
-| [`me_reconnect_backoff_cap_ms`](#me_reconnect_backoff_cap_ms) | `u64` | `30000` |
-| [`me_reconnect_fast_retry_count`](#me_reconnect_fast_retry_count) | `u32` | `16` |
-| [`me_single_endpoint_shadow_writers`](#me_single_endpoint_shadow_writers) | `u8` | `2` |
-| [`me_single_endpoint_outage_mode_enabled`](#me_single_endpoint_outage_mode_enabled) | `bool` | `true` |
-| [`me_single_endpoint_outage_disable_quarantine`](#me_single_endpoint_outage_disable_quarantine) | `bool` | `true` |
-| [`me_single_endpoint_outage_backoff_min_ms`](#me_single_endpoint_outage_backoff_min_ms) | `u64` | `250` |
-| [`me_single_endpoint_outage_backoff_max_ms`](#me_single_endpoint_outage_backoff_max_ms) | `u64` | `3000` |
-| [`me_single_endpoint_shadow_rotate_every_secs`](#me_single_endpoint_shadow_rotate_every_secs) | `u64` | `900` |
-| [`me_floor_mode`](#me_floor_mode) | `"static"` or `"adaptive"` | `"adaptive"` |
-| [`me_adaptive_floor_idle_secs`](#me_adaptive_floor_idle_secs) | `u64` | `90` |
-| [`me_adaptive_floor_min_writers_single_endpoint`](#me_adaptive_floor_min_writers_single_endpoint) | `u8` | `1` |
-| [`me_adaptive_floor_min_writers_multi_endpoint`](#me_adaptive_floor_min_writers_multi_endpoint) | `u8` | `1` |
-| [`me_adaptive_floor_recover_grace_secs`](#me_adaptive_floor_recover_grace_secs) | `u64` | `180` |
-| [`me_adaptive_floor_writers_per_core_total`](#me_adaptive_floor_writers_per_core_total) | `u16` | `48` |
-| [`me_adaptive_floor_cpu_cores_override`](#me_adaptive_floor_cpu_cores_override) | `u16` | `0` |
-| [`me_adaptive_floor_max_extra_writers_single_per_core`](#me_adaptive_floor_max_extra_writers_single_per_core) | `u16` | `1` |
-| [`me_adaptive_floor_max_extra_writers_multi_per_core`](#me_adaptive_floor_max_extra_writers_multi_per_core) | `u16` | `2` |
-| [`me_adaptive_floor_max_active_writers_per_core`](#me_adaptive_floor_max_active_writers_per_core) | `u16` | `64` |
-| [`me_adaptive_floor_max_warm_writers_per_core`](#me_adaptive_floor_max_warm_writers_per_core) | `u16` | `64` |
-| [`me_adaptive_floor_max_active_writers_global`](#me_adaptive_floor_max_active_writers_global) | `u32` | `256` |
-| [`me_adaptive_floor_max_warm_writers_global`](#me_adaptive_floor_max_warm_writers_global) | `u32` | `256` |
-| [`upstream_connect_retry_attempts`](#upstream_connect_retry_attempts) | `u32` | `2` |
-| [`upstream_connect_retry_backoff_ms`](#upstream_connect_retry_backoff_ms) | `u64` | `100` |
-| [`upstream_connect_budget_ms`](#upstream_connect_budget_ms) | `u64` | `3000` |
-| [`upstream_unhealthy_fail_threshold`](#upstream_unhealthy_fail_threshold) | `u32` | `5` |
-| [`upstream_connect_failfast_hard_errors`](#upstream_connect_failfast_hard_errors) | `bool` | `false` |
-| [`stun_iface_mismatch_ignore`](#stun_iface_mismatch_ignore) | `bool` | `false` |
-| [`unknown_dc_log_path`](#unknown_dc_log_path) | `String` | `"unknown-dc.txt"` |
-| [`unknown_dc_file_log_enabled`](#unknown_dc_file_log_enabled) | `bool` | `false` |
-| [`log_level`](#log_level) | `"debug"`, `"verbose"`, `"normal"`, or `"silent"` | `"normal"` |
-| [`disable_colors`](#disable_colors) | `bool` | `false` |
-| [`me_socks_kdf_policy`](#me_socks_kdf_policy) | `"strict"` or `"compat"` | `"strict"` |
-| [`me_route_backpressure_enabled`](#me_route_backpressure_enabled) | `bool` | `false` |
-| [`me_route_fairshare_enabled`](#me_route_fairshare_enabled) | `bool` | `false` |
-| [`me_route_backpressure_base_timeout_ms`](#me_route_backpressure_base_timeout_ms) | `u64` | `25` |
-| [`me_route_backpressure_high_timeout_ms`](#me_route_backpressure_high_timeout_ms) | `u64` | `120` |
-| [`me_route_backpressure_high_watermark_pct`](#me_route_backpressure_high_watermark_pct) | `u8` | `80` |
-| [`me_health_interval_ms_unhealthy`](#me_health_interval_ms_unhealthy) | `u64` | `1000` |
-| [`me_health_interval_ms_healthy`](#me_health_interval_ms_healthy) | `u64` | `3000` |
-| [`me_admission_poll_ms`](#me_admission_poll_ms) | `u64` | `1000` |
-| [`me_warn_rate_limit_ms`](#me_warn_rate_limit_ms) | `u64` | `5000` |
-| [`me_route_no_writer_mode`](#me_route_no_writer_mode) | `"async_recovery_failfast"`, `"inline_recovery_legacy"`, or `"hybrid_async_persistent"` | `"hybrid_async_persistent"` |
-| [`me_route_no_writer_wait_ms`](#me_route_no_writer_wait_ms) | `u64` | `250` |
-| [`me_route_hybrid_max_wait_ms`](#me_route_hybrid_max_wait_ms) | `u64` | `3000` |
-| [`me_route_blocking_send_timeout_ms`](#me_route_blocking_send_timeout_ms) | `u64` | `250` |
-| [`me_route_inline_recovery_attempts`](#me_route_inline_recovery_attempts) | `u32` | `3` |
-| [`me_route_inline_recovery_wait_ms`](#me_route_inline_recovery_wait_ms) | `u64` | `3000` |
-| [`fast_mode_min_tls_record`](#fast_mode_min_tls_record) | `usize` | `0` |
-| [`update_every`](#update_every) | `u64` | `300` |
-| [`me_reinit_every_secs`](#me_reinit_every_secs) | `u64` | `900` |
-| [`me_hardswap_warmup_delay_min_ms`](#me_hardswap_warmup_delay_min_ms) | `u64` | `1000` |
-| [`me_hardswap_warmup_delay_max_ms`](#me_hardswap_warmup_delay_max_ms) | `u64` | `2000` |
-| [`me_hardswap_warmup_extra_passes`](#me_hardswap_warmup_extra_passes) | `u8` | `3` |
-| [`me_hardswap_warmup_pass_backoff_base_ms`](#me_hardswap_warmup_pass_backoff_base_ms) | `u64` | `500` |
-| [`me_config_stable_snapshots`](#me_config_stable_snapshots) | `u8` | `2` |
-| [`me_config_apply_cooldown_secs`](#me_config_apply_cooldown_secs) | `u64` | `300` |
-| [`me_snapshot_require_http_2xx`](#me_snapshot_require_http_2xx) | `bool` | `true` |
-| [`me_snapshot_reject_empty_map`](#me_snapshot_reject_empty_map) | `bool` | `true` |
-| [`me_snapshot_min_proxy_for_lines`](#me_snapshot_min_proxy_for_lines) | `u32` | `1` |
-| [`proxy_secret_stable_snapshots`](#proxy_secret_stable_snapshots) | `u8` | `2` |
-| [`proxy_secret_rotate_runtime`](#proxy_secret_rotate_runtime) | `bool` | `true` |
-| [`me_secret_atomic_snapshot`](#me_secret_atomic_snapshot) | `bool` | `true` |
-| [`proxy_secret_len_max`](#proxy_secret_len_max) | `usize` | `256` |
-| [`me_pool_drain_ttl_secs`](#me_pool_drain_ttl_secs) | `u64` | `90` |
-| [`me_instadrain`](#me_instadrain) | `bool` | `false` |
-| [`me_pool_drain_threshold`](#me_pool_drain_threshold) | `u64` | `32` |
-| [`me_pool_drain_soft_evict_enabled`](#me_pool_drain_soft_evict_enabled) | `bool` | `true` |
-| [`me_pool_drain_soft_evict_grace_secs`](#me_pool_drain_soft_evict_grace_secs) | `u64` | `10` |
-| [`me_pool_drain_soft_evict_per_writer`](#me_pool_drain_soft_evict_per_writer) | `u8` | `2` |
-| [`me_pool_drain_soft_evict_budget_per_core`](#me_pool_drain_soft_evict_budget_per_core) | `u16` | `16` |
-| [`me_pool_drain_soft_evict_cooldown_ms`](#me_pool_drain_soft_evict_cooldown_ms) | `u64` | `1000` |
-| [`me_bind_stale_mode`](#me_bind_stale_mode) | `"never"`, `"ttl"`, or `"always"` | `"ttl"` |
-| [`me_bind_stale_ttl_secs`](#me_bind_stale_ttl_secs) | `u64` | `90` |
-| [`me_pool_min_fresh_ratio`](#me_pool_min_fresh_ratio) | `f32` | `0.8` |
-| [`me_reinit_drain_timeout_secs`](#me_reinit_drain_timeout_secs) | `u64` | `90` |
-| [`proxy_secret_auto_reload_secs`](#proxy_secret_auto_reload_secs) | `u64` | `3600` |
-| [`proxy_config_auto_reload_secs`](#proxy_config_auto_reload_secs) | `u64` | `3600` |
-| [`me_reinit_singleflight`](#me_reinit_singleflight) | `bool` | `true` |
-| [`me_reinit_trigger_channel`](#me_reinit_trigger_channel) | `usize` | `64` |
-| [`me_reinit_coalesce_window_ms`](#me_reinit_coalesce_window_ms) | `u64` | `200` |
-| [`me_deterministic_writer_sort`](#me_deterministic_writer_sort) | `bool` | `true` |
-| [`me_writer_pick_mode`](#me_writer_pick_mode) | `"sorted_rr"` or `"p2c"` | `"p2c"` |
-| [`me_writer_pick_sample_size`](#me_writer_pick_sample_size) | `u8` | `3` |
-| [`ntp_check`](#ntp_check) | `bool` | `true` |
-| [`ntp_servers`](#ntp_servers) | `String[]` | `["pool.ntp.org"]` |
-| [`auto_degradation_enabled`](#auto_degradation_enabled) | `bool` | `true` |
-| [`degradation_min_unavailable_dc_groups`](#degradation_min_unavailable_dc_groups) | `u8` | `2` |
-| [`rst_on_close`](#rst_on_close) | `"off"`, `"errors"` или `"always"` | `"off"` |
+
 | Ключ | Тип | По умолчанию | Hot-Reload |
 | --- | ---- | ------- | ---------- |
 | [`data_path`](#data_path) | `String` | — | `✘` |
@@ -770,7 +632,7 @@
     ```
 ## beobachten
   - **Ограничения / валидация**: `bool`.
-  - **Описание**: Включает "криминалистическое" наблюдения для каждого IP-адреса. Анализирует поведение всех подключений и записывает возможные типы клиентов, которые посылают active-probing запросы.
+  - **Описание**: Включает "криминалистическое" наблюдения для каждого IP-адреса. Анализирует поведение всех подключений, записывает возможные типы клиентов, которые посылают active-probing запросы, и добавляет snapshot’ы TLS JA3/JA4 fingerprint’ов в Beobachten output, когда есть данные.
   - **Пример**:
 
     ```toml
@@ -779,7 +641,7 @@
     ```
 ## beobachten_minutes
   - **Ограничения / валидация**: Должно быть `> 0` (минут).
-  - **Описание**: Время хранения (минуты) для сегментов наблюдения по каждому IP-адресу.
+  - **Описание**: Время хранения (минуты) для сегментов наблюдения по каждому IP-адресу и in-memory bucket’ов TLS fingerprint’ов.
   - **Пример**:
 
     ```toml
@@ -1945,6 +1807,7 @@
 | [`listen_unix_sock`](#listen_unix_sock) | `String` | — | `✘` |
 | [`listen_unix_sock_perm`](#listen_unix_sock_perm) | `String` | — | `✘` |
 | [`listen_tcp`](#listen_tcp) | `bool` | — (auto) | `✘` |
+| [`client_mss`](#client_mss) | `String` | `""` | `✘` |
 | [`proxy_protocol`](#proxy_protocol) | `bool` | `false` | `✘` |
 | [`proxy_protocol_header_timeout_ms`](#proxy_protocol_header_timeout_ms) | `u64` | `500` | `✘` |
 | [`proxy_protocol_trusted_cidrs`](#proxy_protocol_trusted_cidrs) | `IpNetwork[]` | `[]` | `✘` |
@@ -2027,6 +1890,16 @@
     listen_unix_sock = "/run/telemt.sock"
     listen_tcp = true
     ```
+## client_mss
+  - **Ограничения / валидация**: `String`. Пустое значение или отсутствие параметра означает, что Telemt не изменяет MSS, выбранный ядром. Поддерживаемые presets: `"extreme-low"` = `88`, `"tspu"` = `92`, `"2in8"` = `256`. Пользовательское десятичное значение должно быть строкой в диапазоне `88..=4096`.
+  - **Описание**: MSS для входящих TCP-соединений клиентов. Значение применяется к TCP listener-сокетам до `listen(2)`, чтобы Linux мог объявить его в SYN/ACK. Параметр влияет только на proxy client TCP listeners и не применяется к API, metrics, Unix sockets, Telegram upstreams, ME sockets или mask backend connections. Изменение требует restart/rebind listener’ов.
+  - **Performance note**: Низкий MSS предсказуемо увеличивает количество TCP-сегментов. Приблизительный multiplier: `ceil(1460 / client_mss)`.
+  - **Пример**:
+
+    ```toml
+    [server]
+    client_mss = "tspu"
+    ```
 ## proxy_protocol
   - **Ограничения / валидация**: `bool`.
   - **Описание**: Включает поддержку разбора PROXY protocol от HAProxy (v1/v2) на входящих соединениях. При включении исходный IP клиента берётся из PROXY-заголовка.
@@ -2317,7 +2190,7 @@
     ```
 ## runtime_edge_top_n
   - **Ограничения / валидация**: `1..=1000`.
-  - **Описание**: Размер выборки Top-N для рейтинга (leaderboard) edge-соединений.
+  - **Описание**: Размер выборки Top-N для snapshot’ов рейтинга edge-соединений и TLS fingerprint’ов.
   - **Пример**:
 
     ```toml
@@ -2351,6 +2224,11 @@
 | --- | ---- | ------- | ---------- |
 | [`ip`](#ip) | `IpAddr` | — | `✘` |
 | [`port`](#port-serverlisteners) | `u16` | `server.port` | `✘` |
+| [`client_mss`](#client_mss-serverlisteners) | `String` | `[server].client_mss` | `✘` |
+| [`synlimit`](#synlimit-serverlisteners) | `false`, `"iptables"` или `"nftables"` | `false` | `✔` |
+| [`synlimit_seconds`](#synlimit_seconds-serverlisteners) | `u32` | `1` | `✔` |
+| [`synlimit_hitcount`](#synlimit_hitcount-serverlisteners) | `u32` | `1` | `✔` |
+| [`synlimit_burst`](#synlimit_burst-serverlisteners) | `u32` | `2` | `✔` |
 | [`announce`](#announce) | `String` | — | `✘` |
 | [`announce_ip`](#announce_ip) | `IpAddr` | — | `✘` |
 | [`proxy_protocol`](#proxy_protocol) | `bool` | — | `✘` |
@@ -2375,6 +2253,69 @@
     ip = "0.0.0.0"
     port = 443
     ```
+## client_mss (server.listeners)
+  - **Ограничения / валидация**: `String` (необязательный параметр). Допустимые значения совпадают с `[server].client_mss`.
+  - **Описание**: Per-listener override для MSS. Если параметр не задан, listener наследует `[server].client_mss`; если задана пустая строка, MSS shaping отключается только для этого listener’а, даже когда глобальный параметр задан. Изменение требует restart/rebind listener’а.
+  - **Пример**:
+
+    ```toml
+    [[server.listeners]]
+    ip = "0.0.0.0"
+    port = 443
+    client_mss = "256"
+    ```
+## synlimit (server.listeners)
+  - **Ограничения / валидация**: `false`, `"iptables"` или `"nftables"`. Если параметр не задан или задан как `false`, SYN limiter для этого listener’а выключен.
+  - **Описание**: Устанавливает per-listener Linux netfilter SYN limiter rules для порта listener’а. `"iptables"` использует `iptables`/`ip6tables` filter rules с `hashlimit` match как per-source token bucket. `"nftables"` использует per-source `meter` rules с `limit rate over` и автоматически определяет, какие table families уже используются на хосте (`inet`, `ip`, `ip6`), перед созданием Telemt-owned tables. Token-bucket rate равен `synlimit_hitcount / synlimit_seconds`; `synlimit_burst` управляет burst size. Rules reconciled at runtime и удаляются при graceful shutdown Telemt; `SIGKILL` процессом не очищается. Требует CAP_NET_ADMIN. Изменения `synlimit*` hot-reload’ятся для существующих listener endpoints; изменение listener `ip` или `port` по-прежнему требует restart/rebind.
+  - **Пример**:
+
+    ```toml
+    [[server.listeners]]
+    ip = "0.0.0.0"
+    port = 443
+    synlimit = "iptables"
+
+    [[server.listeners]]
+    ip = "::"
+    port = 443
+    synlimit = "nftables"
+    ```
+## synlimit_seconds (server.listeners)
+  - **Ограничения / валидация**: `u32`, должно быть `> 0`. Значение по умолчанию: `1`.
+  - **Описание**: Token-bucket interval для обоих SYN limiter backends. Rate равен `synlimit_hitcount / synlimit_seconds` и рендерится в native netfilter rate units (`second`, `minute`, `hour` или `day`).
+  - **Пример**:
+
+    ```toml
+    [[server.listeners]]
+    ip = "0.0.0.0"
+    port = 443
+    synlimit = "iptables"
+    synlimit_seconds = 1
+    ```
+## synlimit_hitcount (server.listeners)
+  - **Ограничения / валидация**: `u32`, должно быть `> 0`. Значение по умолчанию: `1`.
+  - **Описание**: Token-bucket rate amount для обоих SYN limiter backends. Вместе с `synlimit_seconds` задает разрешенный source-IP SYN rate до того, как excess SYN packets начнут drop’аться.
+  - **Пример**:
+
+    ```toml
+    [[server.listeners]]
+    ip = "0.0.0.0"
+    port = 443
+    synlimit = "iptables"
+    synlimit_hitcount = 1
+    ```
+## synlimit_burst (server.listeners)
+  - **Ограничения / валидация**: `u32`, должно быть `> 0`. Значение по умолчанию: `2`.
+  - **Описание**: Token-bucket burst size для обоих SYN limiter backends. Более высокие значения разрешают short connection bursts с одного source IP перед применением steady-state rate `synlimit_hitcount / synlimit_seconds`.
+  - **Пример**:
+
+    ```toml
+    [[server.listeners]]
+    ip = "0.0.0.0"
+    port = 443
+    synlimit = "iptables"
+    synlimit_burst = 2
+    ```
 ## announce
   - **Ограничения / валидация**: `String` (необязательный параметр). Не должен быть пустым, если задан.
   - **Описание**: Публичный IP-адрес или домен, объявляемый в proxy-ссылках для данного listener’а. Имеет приоритет над `announce_ip`.
@@ -2531,41 +2472,6 @@
 # [censorship]
 
 
-| Ключ | Тип | По умолчанию |
-| --- | ---- | ------- |
-| [`tls_domain`](#tls_domain) | `String` | `"petrovich.ru"` |
-| [`tls_domains`](#tls_domains) | `String[]` | `[]` |
-| [`unknown_sni_action`](#unknown_sni_action) | `"drop"`, `"mask"`, `"accept"`, `"reject_handshake"` | `"drop"` |
-| [`tls_fetch_scope`](#tls_fetch_scope) | `String` | `""` |
-| [`tls_fetch`](#tls_fetch) | `Table` | built-in defaults |
-| [`mask`](#mask) | `bool` | `true` |
-| [`mask_host`](#mask_host) | `String` | — |
-| [`mask_port`](#mask_port) | `u16` | `443` |
-| [`exclusive_mask`](#exclusive_mask) | `Map<String,String>` | `{}` |
-| [`mask_unix_sock`](#mask_unix_sock) | `String` | — |
-| [`fake_cert_len`](#fake_cert_len) | `usize` | `2048` |
-| [`tls_emulation`](#tls_emulation) | `bool` | `true` |
-| [`tls_front_dir`](#tls_front_dir) | `String` | `"tlsfront"` |
-| [`server_hello_delay_min_ms`](#server_hello_delay_min_ms) | `u64` | `0` |
-| [`server_hello_delay_max_ms`](#server_hello_delay_max_ms) | `u64` | `0` |
-| [`tls_new_session_tickets`](#tls_new_session_tickets) | `u8` | `0` |
-| [`tls_full_cert_ttl_secs`](#tls_full_cert_ttl_secs) | `u64` | `90` |
-| [`serverhello_compact`](#serverhello_compact) | `bool` | `false` |
-| [`alpn_enforce`](#alpn_enforce) | `bool` | `true` |
-| [`mask_proxy_protocol`](#mask_proxy_protocol) | `u8` | `0` |
-| [`mask_shape_hardening`](#mask_shape_hardening) | `bool` | `true` |
-| [`mask_shape_hardening_aggressive_mode`](#mask_shape_hardening_aggressive_mode) | `bool` | `false` |
-| [`mask_shape_bucket_floor_bytes`](#mask_shape_bucket_floor_bytes) | `usize` | `512` |
-| [`mask_shape_bucket_cap_bytes`](#mask_shape_bucket_cap_bytes) | `usize` | `4096` |
-| [`mask_shape_above_cap_blur`](#mask_shape_above_cap_blur) | `bool` | `false` |
-| [`mask_shape_above_cap_blur_max_bytes`](#mask_shape_above_cap_blur_max_bytes) | `usize` | `512` |
-| [`mask_relay_max_bytes`](#mask_relay_max_bytes) | `usize` | `5242880` |
-| [`mask_relay_timeout_ms`](mask_relay_timeout_ms) | `u64` | `60_000` |
-| [`mask_relay_idle_timeout_ms`](mask_relay_idle_timeout_ms) | `u64` | `5_000` |
-| [`mask_classifier_prefetch_timeout_ms`](#mask_classifier_prefetch_timeout_ms) | `u64` | `5` |
-| [`mask_timing_normalization_enabled`](#mask_timing_normalization_enabled) | `bool` | `false` |
-| [`mask_timing_normalization_floor_ms`](#mask_timing_normalization_floor_ms) | `u64` | `0` |
-| [`mask_timing_normalization_ceiling_ms`](#mask_timing_normalization_ceiling_ms) | `u64` | `0` |
 | Ключ | Тип | По умолчанию | Hot-Reload |
 | --- | ---- | ------- | ---------- |
 | [`tls_domain`](#tls_domain) | `String` | `"petrovich.ru"` | `✘` |
@@ -3273,7 +3179,7 @@
 
 ## user_rate_limits
   - **Ограничения / валидация**: Таблица `username -> { up_bps, down_bps }`. Должно быть ненулевое значение хотя бы в одном направлении.
-  - **Описание**: Персональные лимиты скорости по пользователям в байтах/сек для отправки (`up_bps`) и получения (`down_bps`).
+  - **Описание**: Персональные лимиты скорости по пользователям в битах/сек для отправки (`up_bps`) и получения (`down_bps`).
   - **Example**:
 
     ```toml
@@ -3300,6 +3206,7 @@
 | [`scopes`](#scopes) | `String` | `""` | `✘` |
 | [`ipv4`](#ipv4-upstreams) | `bool` | — (auto) | `✘` |
 | [`ipv6`](#ipv6-upstreams) | `bool` | — (auto) | `✘` |
+| [`prefer`](#prefer-upstreams) | `4` или `6` | эффективный `[network].prefer` | `✘` |
 | [`interface`](#interface) | `String` | — | `✘` |
 | [`bind_addresses`](#bind_addresses) | `String[]` | — | `✘` |
 | [`bindtodevice`](#bindtodevice) | `String` | — | `✘` |
@@ -3371,7 +3278,7 @@
     ```
 ## ipv6 (upstreams)
   - **Ограничения / валидация**: `bool` (необязательный параметр).
-  - **Описание**: Разрешает IPv6 DC-targets для этого upstream. Если не задан, Telemt определяет поддержку автоматически по runtime-состоянию connectivity.
+  - **Описание**: Разрешает IPv6 DC-targets для этого upstream. Если не задан, Telemt определяет поддержку автоматически по runtime-состоянию connectivity. Установите `true`, если upstream proxy доступен с локального хоста по IPv4, но сам proxy умеет подключаться к Telegram DC по IPv6.
   - **Пример**:
 
     ```toml
@@ -3379,6 +3286,18 @@
     type = "direct"
     ipv6 = false
     ```
+## prefer (upstreams)
+  - **Ограничения / валидация**: Необязательное число. Должно быть `4` или `6`.
+  - **Описание**: Переопределяет предпочтительное IP-семейство для Telegram DC-targets, выбранных через этот upstream. Если параметр не задан, upstream наследует эффективное глобальное решение `[network].prefer`. Используйте `prefer = 6` вместе с `ipv6 = true` для SOCKS или Shadowsocks upstream, который умеет выходить в IPv6, даже если локальный хост с Telemt работает только по IPv4.
+  - **Пример**:
+
+    ```toml
+    [[upstreams]]
+    type = "socks5"
+    address = "192.0.2.10:1080"
+    ipv6 = true
+    prefer = 6
+    ```
 ## interface
   - **Ограничения / валидация**: `String` (необязательный параметр).
     - для `"direct"`: может быть IP-адресом (используется как явный local bind) или именем сетевого интерфейса ОС (резолвится в IP во время выполнения; только Unix).

docs/FAQ.en.md

@@ -172,7 +172,7 @@ Those cross-DC requests are normal and happen constantly.
 > If your home DC is DC2 and DC2 goes down, you **cannot** reach DC5 even though DC5 itself is perfectly healthy.  
 > The client has no valid session to route the request through.  
 
-This is also why an MTProxy only needs to reach Telegram's DC infrastructure as a whole.  
+This is also why it is required for MTProxy to reach Telegram's DC infrastructure as a whole.  
 The proxy itself doesn't care which DC your account lives on. The client negotiates the correct DC through the proxy after connecting.
 
 ### How many people can use one link

docs/FAQ.ru.md

@@ -40,6 +40,8 @@ hello2 = "ad_tag2"
 > Проблема с TLS отпечатком исправлена в последних версиях клиентов Telegram для Desktop / Android / iOS.  
 > Обновите свой клиент для корректной работы с MTProxy Fake-TLS!
 
+- Для расследования блокировок на базе JA4 ClientHello используйте отдельную инструкцию: [`JA3 и JA4 анализ в Telemt`](Architecture/Fronting-splitting/TLS_JA3_JA4_ANALYSIS.ru.md).
+
 - Мы считаем это прорывом, которому на сегодняшний день нет стабильных аналогов;
 - Исходя из этого: если `telemt` настроен правильно, **режим TLS полностью идентичен реальному «рукопожатию» + обмену данными** с указанным хостом;
 - Вот наши доказательства:
@@ -157,7 +159,7 @@ https://github.com/telemt/telemt/discussions/167
 
 ## Как клиенты взаимодействуют с дата-центрами Telegram
 При регистрации аккаунта Telegram он навсегда привязывается к одному из дата-центров (DC).  
-Telegram заранее определяет к какому DC привязать аккаунт исходя из региона, к которому относиться номер телефона.  
+Telegram заранее определяет к какому DC привязать аккаунт исходя из региона, к которому относится номер телефона.  
 Этот DC становится вашим **домашним**: именно там хранится весь контент, который вы загружаете (фото, видео, файлы, сообщения).  
 И именно на нем клиент авторизуется при каждом подключении.  
 
@@ -170,7 +172,7 @@ Telegram заранее определяет к какому DC привязат
 > Если ваш домашний DC — DC2, и DC2 лежит, вы **не сможете** достучаться  и до DC5, даже если сам DC5 полностью исправен.  
 > У клиента просто нет валидной сессии, через которую можно было бы направить запрос.  
 
-По той же причине MTProxy достаточно иметь доступ к инфраструктуре Telegram в целом.  
+По той же причине MTProxy необходимо иметь доступ к инфраструктуре Telegram целиком, а не частично.  
 Cамому MTProxy всё равно, на каком DC живёт ваш аккаунт. Клиент cам договаривается о нужном DC через прокси уже после подключения.  
 
 ## Что такое dd и ee в контексте MTProxy?

docs/Quick_start/QUICK_START_GUIDE.ru.md

@@ -235,7 +235,10 @@ curl -s http://127.0.0.1:9091/v1/users | jq -r '.data[] | "[\(.username)]", (.li
 
 # Telemt через Docker Compose
 
-**1. Отредактируйте `config.toml` в корневом каталоге репозитория (как минимум: порт, пользовательские секреты, tls_domain)**  
+**1. Создайте директорию `config/` и поместите в неё отрдеактированный `config.toml` (указав как минимум: порт, пользовательские секреты, tls_domain):**
+```bash
+mkdir config && mv config.toml config/
+```
 **2. Запустите контейнер:**
 ```bash
 docker compose up -d --build
@@ -249,7 +252,7 @@ docker compose logs -f telemt
 docker compose down
 ```
 > [!NOTE]
-> - В `docker-compose.yml` файл `./config.toml` монтируется в `/app/config.toml` (доступно только для чтения)  
+> - Директория `./config/` монтируется в `/etc/telemt/` (read-write), что позволяет API атомарно обновлять config.toml
 > - По умолчанию публикуются порты 443:443, а контейнер запускается со сброшенными привилегиями (добавлена только `NET_BIND_SERVICE`)  
 > - Если вам действительно нужна сеть хоста (обычно это требуется только для некоторых конфигураций IPv6), раскомментируйте `network_mode: host`
 

docs/Setup_examples/XRAY_DOUBLE_HOP.en.md

@@ -206,7 +206,7 @@ File content:
           "publicKey": "<SERVER_B_PUBLIC_KEY>",
           "shortId": "<SHORT_ID>",
           "spiderX": "/",
-          "fingerprint": "chrome"
+          "fingerprint": "firefox"
         },
         "xhttpSettings": {
           "path": "/<YOUR_RANDOM_PATH>"

docs/Setup_examples/XRAY_DOUBLE_HOP.ru.md

@@ -206,7 +206,7 @@ nano /usr/local/etc/xray/config.json
           "publicKey": "<SERVER_B_PUBLIC_KEY>",
           "shortId": "<SHORT_ID>",
           "spiderX": "/",
-          "fingerprint": "chrome"
+          "fingerprint": "firefox"
         },
         "xhttpSettings": {
           "path": "/<YOUR_RANDOM_PATH>"

install.sh

@@ -84,21 +84,22 @@ set_language() {
             L_INFO_KEEP_CONF="Примечание: Конфигурация сохранена. Используйте 'purge' для очистки."
             L_INFO_I_START="Начинается установка"
             L_I_STAGE_1=">>> Этап 1: Проверка окружения и зависимостей"
-            L_I_STAGE_1_5=">>> Этап 1.5: Интерактивная настройка"
+            L_I_STAGE_2=">>> Этап 2: Интерактивная настройка"
             L_I_PROMPT_DOM="\nПожалуйста, укажите домен TLS\nНажмите Enter, чтобы оставить по умолчанию [%s]: "
+            L_I_PROMPT_PORT="\nПожалуйста, укажите порт сервера\nНажмите Enter, чтобы оставить по умолчанию [%s]: "
             L_WARN_NO_TTY="Интерактивный режим недоступен (нет TTY). Используется:"
-            L_I_STAGE_2=">>> Этап 2: Загрузка архива"
+            L_I_STAGE_3=">>> Этап 3: Загрузка архива"
             L_ERR_TMP_DIR="Не удалось создать временную директорию"
             L_ERR_TMP_INV="Временная директория недействительна"
             L_INFO_FALLBACK="Сборка x86_64-v3 не найдена, откат к стандартной x86_64..."
             L_ERR_DL_FAIL="Ошибка загрузки архива"
-            L_I_STAGE_3=">>> Этап 3: Распаковка архива"
+            L_I_STAGE_4=">>> Этап 4: Распаковка архива"
             L_ERR_EXTRACT="Ошибка распаковки архива."
             L_ERR_BIN_NOT_FOUND="Бинарный файл не найден в архиве"
-            L_I_STAGE_4=">>> Этап 4: Настройка окружения (Юзер, Группа, Папки)"
-            L_I_STAGE_5=">>> Этап 5: Установка бинарного файла"
-            L_I_STAGE_6=">>> Этап 6: Генерация/Обновление конфигурации"
-            L_I_STAGE_7=">>> Этап 7: Установка и запуск службы"
+            L_I_STAGE_5=">>> Этап 5: Настройка окружения (Юзер, Группа, Папки)"
+            L_I_STAGE_6=">>> Этап 6: Установка бинарного файла"
+            L_I_STAGE_7=">>> Этап 7: Генерация/Обновление конфигурации"
+            L_I_STAGE_8=">>> Этап 8: Установка и запуск службы"
             L_OUT_WARN_H="УСТАНОВКА ЗАВЕРШЕНА С ПРЕДУПРЕЖДЕНИЯМИ"
             L_OUT_WARN_D="Служба установлена, но не запустилась.\nПожалуйста, проверьте логи.\n"
             L_OUT_SUCC_H="УСТАНОВКА УСПЕШНО ЗАВЕРШЕНА"
@@ -160,21 +161,22 @@ set_language() {
             L_INFO_KEEP_CONF="Note: Configuration kept. Run with 'purge' to remove completely."
             L_INFO_I_START="Starting installation of"
             L_I_STAGE_1=">>> Stage 1: Verifying environment and dependencies"
-            L_I_STAGE_1_5=">>> Stage 1.5: Interactive Setup"
+            L_I_STAGE_2=">>> Stage 2: Interactive Setup"
             L_I_PROMPT_DOM="\nPlease specify the TLS Domain\nPress Enter to keep default [%s]: "
+            L_I_PROMPT_PORT="\nPlease specify the Server Port\nPress Enter to keep default [%s]: "
             L_WARN_NO_TTY="Interactive mode unavailable (no TTY). Using:"
-            L_I_STAGE_2=">>> Stage 2: Downloading archive"
+            L_I_STAGE_3=">>> Stage 3: Downloading archive"
             L_ERR_TMP_DIR="Temp directory creation failed"
             L_ERR_TMP_INV="Temp directory is invalid or was not created"
             L_INFO_FALLBACK="x86_64-v3 build not found, falling back to standard x86_64..."
             L_ERR_DL_FAIL="Download failed"
-            L_I_STAGE_3=">>> Stage 3: Extracting archive"
+            L_I_STAGE_4=">>> Stage 4: Extracting archive"
             L_ERR_EXTRACT="Extraction failed."
             L_ERR_BIN_NOT_FOUND="Binary not found in archive"
-            L_I_STAGE_4=">>> Stage 4: Setting up environment (User, Group, Directories)"
-            L_I_STAGE_5=">>> Stage 5: Installing binary"
-            L_I_STAGE_6=">>> Stage 6: Generating/Updating configuration"
-            L_I_STAGE_7=">>> Stage 7: Installing and starting service"
+            L_I_STAGE_5=">>> Stage 5: Setting up environment (User, Group, Directories)"
+            L_I_STAGE_6=">>> Stage 6: Installing binary"
+            L_I_STAGE_7=">>> Stage 7: Generating/Updating configuration"
+            L_I_STAGE_8=">>> Stage 8: Installing and starting service"
             L_OUT_WARN_H="INSTALLATION COMPLETED WITH WARNINGS"
             L_OUT_WARN_D="The service was installed but failed to start.\nPlease check the logs to determine the issue.\n"
             L_OUT_SUCC_H="INSTALLATION SUCCESS"
@@ -269,7 +271,10 @@ say() {
     if [ "$#" -eq 0 ] || [ -z "${1:-}" ]; then
         printf '\n'
     else
-        printf '[INFO] %s\n' "$*"
+        case "$*" in
+            \[*\]*) printf '%s\n' "$*" ;;
+            *) printf '[INFO] %s\n' "$*" ;;
+        esac
     fi
 }
 die() { printf '[ERROR] %s\n' "$*" >&2; exit 1; }
@@ -527,9 +532,9 @@ setup_dirs() {
 
 stop_service() {
     svc="$(get_svc_mgr)"
-    if [ "$svc" = "systemd" ] && systemctl is-active --quiet "$SERVICE_NAME" 2>/dev/null; then
+    if [ "$svc" = "systemd" ] && $SUDO systemctl is-active --quiet "$SERVICE_NAME" 2>/dev/null; then
         $SUDO systemctl stop "$SERVICE_NAME" 2>/dev/null || true
-    elif [ "$svc" = "openrc" ] && rc-service "$SERVICE_NAME" status >/dev/null 2>&1; then
+    elif [ "$svc" = "openrc" ] && $SUDO rc-service "$SERVICE_NAME" status >/dev/null 2>&1; then
         $SUDO rc-service "$SERVICE_NAME" stop 2>/dev/null || true
     fi
 }
@@ -832,10 +837,36 @@ case "$ACTION" in
             fi
         fi
 
-        check_port_availability
+        if [ "$PORT_PROVIDED" -eq 0 ] || [ "$DOMAIN_PROVIDED" -eq 0 ]; then
+            say "$L_I_STAGE_2"
+        fi
+
+        if [ "$PORT_PROVIDED" -eq 0 ]; then
+            if [ -t 0 ] || [ -c /dev/tty ]; then
+                while true; do
+                    printf "$L_I_PROMPT_PORT" "$SERVER_PORT"
+                    read -r input_port </dev/tty || input_port=""
+                    if [ -z "$input_port" ]; then
+                        break
+                    fi
+                    case "$input_port" in
+                        *[!0-9]*) printf '[ERROR] %s\n' "$L_ERR_PORT_NUM" >&2; continue ;;
+                    esac
+                    port_num="$(printf '%s\n' "$input_port" | sed 's/^0*//')"
+                    [ -z "$port_num" ] && port_num="0"
+                    if [ "${#port_num}" -gt 5 ] || [ "$port_num" -lt 1 ] || [ "$port_num" -gt 65535 ]; then
+                        printf '[ERROR] %s\n' "$L_ERR_PORT_RANGE" >&2; continue
+                    fi
+                    SERVER_PORT="$port_num"
+                    break
+                done
+            else
+                say "[WARNING] $L_WARN_NO_TTY $SERVER_PORT"
+            fi
+            PORT_PROVIDED=1
+        fi
 
         if [ "$DOMAIN_PROVIDED" -eq 0 ]; then
-            say "$L_I_STAGE_1_5"
             if [ -t 0 ] || [ -c /dev/tty ]; then
                 printf "$L_I_PROMPT_DOM" "$TLS_DOMAIN"
                 read -r input_domain </dev/tty || input_domain=""
@@ -848,6 +879,8 @@ case "$ACTION" in
             DOMAIN_PROVIDED=1
         fi
 
+        check_port_availability
+
         if [ "$TARGET_VERSION" != "latest" ]; then
             TARGET_VERSION="${TARGET_VERSION#v}"
         fi
@@ -861,7 +894,7 @@ case "$ACTION" in
             DL_URL="https://github.com/${REPO}/releases/download/${TARGET_VERSION}/${FILE_NAME}"
         fi
 
-        say "$L_I_STAGE_2"
+        say "$L_I_STAGE_3"
         TEMP_DIR="$(mktemp -d)" || die "$L_ERR_TMP_DIR"
         if [ -z "$TEMP_DIR" ] || [ ! -d "$TEMP_DIR" ]; then
             die "$L_ERR_TMP_INV"
@@ -883,7 +916,7 @@ case "$ACTION" in
             fi
         fi
 
-        say "$L_I_STAGE_3"
+        say "$L_I_STAGE_4"
         if ! gzip -dc "${TEMP_DIR}/${FILE_NAME}" | tar -xf - -C "$TEMP_DIR" 2>/dev/null; then
             die "$L_ERR_EXTRACT"
         fi
@@ -891,16 +924,16 @@ case "$ACTION" in
         EXTRACTED_BIN="$(find "$TEMP_DIR" -type f -name "$BIN_NAME" -print 2>/dev/null | head -n 1 || true)"
         [ -n "$EXTRACTED_BIN" ] || die "$L_ERR_BIN_NOT_FOUND"
 
-        say "$L_I_STAGE_4"
+        say "$L_I_STAGE_5"
         ensure_user_group; setup_dirs; stop_service
 
-        say "$L_I_STAGE_5"
+        say "$L_I_STAGE_6"
         install_binary "$EXTRACTED_BIN" "${INSTALL_DIR}/${BIN_NAME}"
 
-        say "$L_I_STAGE_6"
+        say "$L_I_STAGE_7"
         install_config
 
-        say "$L_I_STAGE_7"
+        say "$L_I_STAGE_8"
         install_service
 
         if [ "${SERVICE_START_FAILED:-0}" -eq 1 ]; then

src/api/config_edit.rs

@@ -0,0 +1,411 @@
+//! Config-editing API: read managed sections and apply sparse field patches.
+//! `access.*` is intentionally not editable here (owned by the users API).
+
+use serde_json::Value as Json;
+use toml::Value as Toml;
+
+use super::ApiShared;
+use super::config_store::{
+    EDITABLE_SECTIONS, compute_revision, current_revision, save_sections_to_disk,
+};
+use super::model::ApiFailure;
+use crate::config::ProxyConfig;
+use crate::config::hot_reload::classify_config_changes;
+use serde::Serialize;
+use std::path::Path;
+
+#[derive(Debug, Serialize)]
+pub(super) struct PatchConfigResponse {
+    pub revision: String,
+    pub restart_required: bool,
+    pub changed: Vec<String>,
+}
+
+/// Shared-state wrapper around [`apply_patch_to_path`]: serializes config
+/// mutations behind `mutation_lock`, then records a runtime event. The route
+/// handler calls this; the core logic stays decoupled for unit tests.
+pub(super) async fn patch_config(
+    patch_json: Json,
+    expected_revision: Option<String>,
+    shared: &ApiShared,
+) -> Result<PatchConfigResponse, ApiFailure> {
+    let _guard = shared.mutation_lock.lock().await;
+    let resp = apply_patch_to_path(&shared.config_path, &patch_json, expected_revision).await?;
+    drop(_guard);
+    shared
+        .runtime_events
+        .record("api.config.patch.ok", format!("changed={:?}", resp.changed));
+    Ok(resp)
+}
+
+/// Core patch logic, decoupled from hyper/shared-state so it is unit-testable
+/// against a temp file. The route handler holds `mutation_lock` while calling this.
+pub(super) async fn apply_patch_to_path(
+    config_path: &Path,
+    patch_json: &Json,
+    expected_revision: Option<String>,
+) -> Result<PatchConfigResponse, ApiFailure> {
+    // 1. optimistic concurrency
+    let current = current_revision(config_path).await?;
+    if expected_revision.is_some_and(|expected| expected != current) {
+        return Err(ApiFailure::new(
+            hyper::StatusCode::CONFLICT,
+            "revision_conflict",
+            "Config revision mismatch",
+        ));
+    }
+
+    // 2. convert + reject access / unknown sections
+    let patch_toml = json_to_toml(patch_json)
+        .map_err(|e| ApiFailure::bad_request(format!("invalid patch: {}", e)))?;
+    let patch_table = patch_toml
+        .as_table()
+        .ok_or_else(|| ApiFailure::bad_request("patch must be a JSON object"))?;
+    if patch_table.contains_key("access") {
+        return Err(ApiFailure::new(
+            hyper::StatusCode::BAD_REQUEST,
+            "access_not_editable",
+            "access.* is managed via the users API, not editable here",
+        ));
+    }
+    for key in patch_table.keys() {
+        if !EDITABLE_SECTIONS.contains(&key.as_str()) {
+            return Err(ApiFailure::new(
+                hyper::StatusCode::BAD_REQUEST,
+                "section_not_editable",
+                format!("section not editable: {}", key),
+            ));
+        }
+    }
+    let touched: Vec<&str> = patch_table
+        .keys()
+        .map(|k| k.as_str())
+        .filter(|k| EDITABLE_SECTIONS.contains(k))
+        .collect();
+    if touched.is_empty() {
+        return Err(ApiFailure::bad_request("empty patch: no editable sections"));
+    }
+
+    // 3. Parse old + merged from the SAME deserialize path so the classifier
+    //    sees only the delta this patch introduces. `ProxyConfig::load` applies
+    //    include-expansion / legacy-compat / normalization that a bare
+    //    `try_into` does not; mixing the two paths would make unrelated fields
+    //    compare unequal and spuriously force `restart_required`.
+    let original = tokio::fs::read_to_string(config_path)
+        .await
+        .map_err(|e| ApiFailure::internal(format!("failed to read config: {}", e)))?;
+    let original_toml: Toml = toml::from_str(&original)
+        .map_err(|e| ApiFailure::internal(format!("failed to parse config: {}", e)))?;
+    let old_cfg: ProxyConfig = original_toml
+        .clone()
+        .try_into()
+        .map_err(|e| ApiFailure::internal(format!("config does not deserialize: {}", e)))?;
+
+    let mut merged = original_toml;
+    deep_merge(&mut merged, &patch_toml);
+
+    let new_cfg: ProxyConfig = merged
+        .clone()
+        .try_into()
+        .map_err(|e| ApiFailure::bad_request(format!("config does not deserialize: {}", e)))?;
+    new_cfg
+        .validate()
+        .map_err(|e| ApiFailure::bad_request(format!("config validation failed: {}", e)))?;
+
+    // 4. classify changes (Telemt's own hot/restart rule)
+    let class = classify_config_changes(&old_cfg, &new_cfg);
+
+    // 5. write only the touched top-level sections
+    let revision = save_sections_to_disk(config_path, &new_cfg, &touched).await?;
+
+    Ok(PatchConfigResponse {
+        revision,
+        restart_required: class.restart_required,
+        changed: class.changed,
+    })
+}
+
+/// Return only the editable config sections + current revision.
+pub(super) async fn read_managed_config(config_path: &Path) -> Result<(Toml, String), ApiFailure> {
+    let original = tokio::fs::read_to_string(config_path)
+        .await
+        .map_err(|e| ApiFailure::internal(format!("failed to read config: {}", e)))?;
+    let parsed: Toml = toml::from_str(&original)
+        .map_err(|e| ApiFailure::internal(format!("failed to parse config: {}", e)))?;
+
+    let parsed_table = parsed
+        .as_table()
+        .cloned()
+        .unwrap_or_else(toml::value::Table::new);
+    // Whitelist: return ONLY the editable sections. A blacklist (just removing
+    // `access`) would leak `server` (carries the API `auth_header` + per-node
+    // identity) and `network` (per-node addresses). Mirror the PATCH contract.
+    let mut table = toml::value::Table::new();
+    for section in EDITABLE_SECTIONS {
+        if let Some(value) = parsed_table.get(*section) {
+            table.insert((*section).to_string(), value.clone());
+        }
+    }
+
+    let revision = compute_revision(&original);
+    Ok((Toml::Table(table), revision))
+}
+
+/// Convert a serde_json value to a toml value. `null` is dropped from objects
+/// (a patch never sets a key to TOML-null). Numbers become integers when exact,
+/// otherwise floats.
+fn json_to_toml(j: &Json) -> Result<Toml, String> {
+    Ok(match j {
+        Json::Null => return Err("null is not representable in TOML".into()),
+        Json::Bool(b) => Toml::Boolean(*b),
+        Json::Number(n) => {
+            if let Some(i) = n.as_i64() {
+                Toml::Integer(i)
+            } else if let Some(f) = n.as_f64() {
+                Toml::Float(f)
+            } else {
+                return Err(format!("unrepresentable number: {}", n));
+            }
+        }
+        Json::String(s) => Toml::String(s.clone()),
+        Json::Array(items) => {
+            let mut out = Vec::with_capacity(items.len());
+            for item in items {
+                out.push(json_to_toml(item)?);
+            }
+            Toml::Array(out)
+        }
+        Json::Object(map) => {
+            let mut table = toml::value::Table::new();
+            for (k, v) in map {
+                if v.is_null() {
+                    continue; // skip nulls instead of erroring at object level
+                }
+                table.insert(k.clone(), json_to_toml(v)?);
+            }
+            Toml::Table(table)
+        }
+    })
+}
+
+/// Recursively overlay `patch` onto `base`. Tables merge key-by-key; every
+/// other value type (scalars, arrays) replaces wholesale.
+fn deep_merge(base: &mut Toml, patch: &Toml) {
+    match (base, patch) {
+        (Toml::Table(b), Toml::Table(p)) => {
+            for (k, pv) in p {
+                match b.get_mut(k) {
+                    Some(bv) => deep_merge(bv, pv),
+                    None => {
+                        b.insert(k.clone(), pv.clone());
+                    }
+                }
+            }
+        }
+        (b, p) => *b = p.clone(),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn json_object_converts_to_toml_table() {
+        let j: Json = serde_json::json!({"censorship": {"tls_domain": "a.com"}, "default_dc": 2});
+        let t = json_to_toml(&j).expect("convertible");
+        let table = t.as_table().unwrap();
+        assert_eq!(table["censorship"]["tls_domain"].as_str(), Some("a.com"));
+        assert_eq!(table["default_dc"].as_integer(), Some(2));
+    }
+
+    #[test]
+    fn deep_merge_overlays_tables_and_replaces_scalars() {
+        let mut base: Toml =
+            toml::from_str("[censorship]\ntls_domain = \"old\"\nfake_cert_len = 100\n").unwrap();
+        let patch: Toml = toml::from_str("[censorship]\ntls_domain = \"new\"\n").unwrap();
+
+        deep_merge(&mut base, &patch);
+
+        let cens = base["censorship"].as_table().unwrap();
+        assert_eq!(cens["tls_domain"].as_str(), Some("new")); // overlaid
+        assert_eq!(cens["fake_cert_len"].as_integer(), Some(100)); // preserved
+    }
+
+    use std::path::PathBuf;
+
+    fn temp_config(body: &str) -> (PathBuf, tempfile::TempDir) {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("config.toml");
+        std::fs::write(&path, body).unwrap();
+        (path, dir)
+    }
+
+    #[tokio::test]
+    async fn patch_rejects_access_section() {
+        let (path, _d) = temp_config("[censorship]\ntls_domain = \"a\"\n");
+        let patch: Json = serde_json::json!({"access": {"users": {"x": "y"}}});
+        let err = apply_patch_to_path(&path, &patch, None).await.unwrap_err();
+        assert_eq!(err.code, "access_not_editable");
+    }
+
+    #[tokio::test]
+    async fn patch_revision_conflict() {
+        let (path, _d) = temp_config("[censorship]\ntls_domain = \"a\"\n");
+        let patch: Json = serde_json::json!({"censorship": {"tls_domain": "b"}});
+        let err = apply_patch_to_path(&path, &patch, Some("deadbeef".into()))
+            .await
+            .unwrap_err();
+        assert_eq!(err.code, "revision_conflict");
+    }
+
+    #[tokio::test]
+    async fn patch_sni_reports_restart_required() {
+        let (path, _d) =
+            temp_config("[censorship]\ntls_domain = \"a.com\"\n[server]\nport = 443\n");
+        let patch: Json = serde_json::json!({"censorship": {"tls_domain": "b.com"}});
+        let resp = apply_patch_to_path(&path, &patch, None).await.unwrap();
+        assert!(resp.restart_required);
+        assert!(resp.changed.iter().any(|c| c == "censorship"));
+        let written = std::fs::read_to_string(&path).unwrap();
+        assert!(written.contains("tls_domain = \"b.com\""));
+        assert_eq!(
+            resp.revision,
+            crate::api::config_store::compute_revision(&written)
+        );
+    }
+
+    #[tokio::test]
+    async fn read_managed_config_strips_access() {
+        let (path, _d) = temp_config(
+            "[censorship]\ntls_domain = \"a.com\"\n[access.users]\nbob = \"deadbeef\"\n",
+        );
+        let (value, revision) = read_managed_config(&path).await.unwrap();
+        let table = value.as_table().unwrap();
+        assert!(table.contains_key("censorship"));
+        assert!(!table.contains_key("access")); // secrets never leave the box here
+        assert_eq!(revision, current_revision(&path).await.unwrap());
+    }
+
+    #[tokio::test]
+    async fn read_managed_config_returns_only_editable_sections() {
+        // server carries the API auth_header + per-node identity; network carries
+        // per-node addresses. Neither must be exposed by GET /v1/config.
+        let (path, _d) = temp_config(concat!(
+            "[censorship]\ntls_domain = \"a\"\n",
+            "[server]\nport = 443\n[server.api]\nauth_header = \"SECRET\"\n",
+            "[network]\nipv4 = \"1.2.3.4\"\n",
+            "[access.users]\nbob = \"deadbeef\"\n",
+        ));
+        let (value, _rev) = read_managed_config(&path).await.unwrap();
+        let table = value.as_table().unwrap();
+        assert!(table.contains_key("censorship"));
+        assert!(!table.contains_key("server")); // no API auth_header / identity leak
+        assert!(!table.contains_key("network")); // no per-node identity leak
+        assert!(!table.contains_key("access")); // no users/secrets
+    }
+
+    #[tokio::test]
+    async fn patch_rejects_server_section() {
+        let (path, _d) = temp_config("[censorship]\ntls_domain = \"a\"\n");
+        let patch: Json = serde_json::json!({"server": {"port": 1}});
+        let err = apply_patch_to_path(&path, &patch, None).await.unwrap_err();
+        assert_eq!(err.code, "section_not_editable");
+    }
+
+    #[tokio::test]
+    async fn patch_rejects_show_link_section() {
+        // show_link is a legacy top-level scalar/array (not a [table]); it cannot
+        // be upserted safely and is superseded by the editable general.links.show.
+        let (path, _d) = temp_config("[censorship]\ntls_domain = \"a\"\n");
+        let patch: Json = serde_json::json!({"show_link": "*"});
+        let err = apply_patch_to_path(&path, &patch, None).await.unwrap_err();
+        assert_eq!(err.code, "section_not_editable");
+    }
+
+    #[tokio::test]
+    async fn patch_general_links_show_is_editable() {
+        // The supported replacement path: edit show via the general.links sub-table.
+        let (path, _d) = temp_config(
+            "[general]\nprefer_ipv6 = false\n[general.links]\nshow = \"*\"\n\
+             [censorship]\ntls_domain = \"a\"\n",
+        );
+        let patch: Json = serde_json::json!({"general": {"links": {"show": ["alice"]}}});
+        let resp = apply_patch_to_path(&path, &patch, None).await.unwrap();
+        assert!(resp.changed.iter().any(|c| c == "general"));
+        let written = tokio::fs::read_to_string(&path).await.unwrap();
+        let parsed: toml::Value = toml::from_str(&written).unwrap();
+        assert_eq!(
+            parsed["general"]["links"]["show"][0].as_str(),
+            Some("alice"),
+            "{written}"
+        );
+        // No leaked top-level [links]/[modes] and no duplicate sub-tables.
+        assert_eq!(written.matches("[general.links]").count(), 1, "{written}");
+    }
+
+    #[tokio::test]
+    async fn patch_links_public_port_written_as_integer_not_float_or_string() {
+        // A JSON integer must land on disk as a bare TOML integer (443), never
+        // 443.0 nor "443". The write re-renders from the typed config, so the
+        // u16 field dictates the output format regardless of JSON quirks.
+        let (path, _d) = temp_config("[general]\nprefer_ipv6 = false\n");
+        let patch: Json = serde_json::json!({"general": {"links": {"public_port": 443}}});
+        apply_patch_to_path(&path, &patch, None).await.unwrap();
+
+        let written = tokio::fs::read_to_string(&path).await.unwrap();
+        assert!(written.contains("public_port = 443"), "{written}");
+        assert!(
+            !written.contains("443.0"),
+            "must not be a float:\n{written}"
+        );
+        assert!(
+            !written.contains("\"443\""),
+            "must not be a string:\n{written}"
+        );
+
+        let parsed: toml::Value = toml::from_str(&written).unwrap();
+        assert_eq!(
+            parsed["general"]["links"]["public_port"].as_integer(),
+            Some(443),
+            "{written}"
+        );
+    }
+
+    #[tokio::test]
+    async fn patch_links_public_port_rejects_float() {
+        // 443.0 cannot deserialize into u16 -> rejected, not silently coerced.
+        let (path, _d) = temp_config("[general]\nprefer_ipv6 = false\n");
+        let patch: Json = serde_json::json!({"general": {"links": {"public_port": 443.0}}});
+        let err = apply_patch_to_path(&path, &patch, None).await.unwrap_err();
+        assert_eq!(err.status, hyper::StatusCode::BAD_REQUEST, "{:?}", err);
+    }
+
+    #[tokio::test]
+    async fn patch_links_public_port_rejects_string() {
+        // "443" is a string, not a u16 -> rejected.
+        let (path, _d) = temp_config("[general]\nprefer_ipv6 = false\n");
+        let patch: Json = serde_json::json!({"general": {"links": {"public_port": "443"}}});
+        let err = apply_patch_to_path(&path, &patch, None).await.unwrap_err();
+        assert_eq!(err.status, hyper::StatusCode::BAD_REQUEST, "{:?}", err);
+    }
+
+    #[tokio::test]
+    async fn patch_empty_is_rejected() {
+        let (path, _d) = temp_config("[censorship]\ntls_domain = \"a\"\n");
+        let patch: Json = serde_json::json!({});
+        assert!(apply_patch_to_path(&path, &patch, None).await.is_err());
+    }
+
+    #[tokio::test]
+    async fn patch_log_level_is_hot() {
+        // general.log_level is hot-reloadable -> a patch changing only it must
+        // report restart_required = false (exercises the full apply path, not
+        // just the classifier). Default LogLevel is Normal; patch to "debug".
+        let (path, _d) = temp_config("[censorship]\ntls_domain = \"a\"\n");
+        let patch: Json = serde_json::json!({"general": {"log_level": "debug"}});
+        let resp = apply_patch_to_path(&path, &patch, None).await.unwrap();
+        assert!(!resp.restart_required);
+        assert!(resp.changed.iter().any(|c| c == "general"));
+    }
+}

src/api/config_store.rs

@@ -14,6 +14,7 @@ use super::model::ApiFailure;
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub(super) enum AccessSection {
     Users,
+    UserEnabled,
     UserAdTags,
     UserMaxTcpConns,
     UserExpirations,
@@ -26,6 +27,7 @@ impl AccessSection {
     fn table_name(self) -> &'static str {
         match self {
             Self::Users => "access.users",
+            Self::UserEnabled => "access.user_enabled",
             Self::UserAdTags => "access.user_ad_tags",
             Self::UserMaxTcpConns => "access.user_max_tcp_conns",
             Self::UserExpirations => "access.user_expirations",
@@ -95,6 +97,90 @@ pub(super) async fn save_config_to_disk(
     Ok(compute_revision(&serialized))
 }
 
+/// Top-level config tables that may be edited via the config API.
+///
+/// Intentionally excluded (defense-in-depth, enforces the spec's per-node
+/// identity invariant at the Telemt layer too):
+///
+///   - `access`    : owned by the users API.
+///   - `server`    : carries per-node identity (`port`, `api`/`api_bind`, listeners).
+///   - `network`   : carries per-node identity (`ipv4`/`ipv6`).
+///   - `show_link` : legacy top-level scalar/array (not a `[table]`), superseded
+///                   by the editable `general.links.show` sub-table. The
+///                   section-upsert machinery here only handles `[table]` /
+///                   `[[array-of-tables]]` blocks; a bare top-level key cannot be
+///                   located or replaced safely, so it is edited via `general`.
+///
+/// A future field-level allowlist can re-admit specific safe fields
+/// (e.g. `network.dns_overrides`) without opening the whole section.
+pub(super) const EDITABLE_SECTIONS: &[&str] = &[
+    "general",
+    "timeouts",
+    "censorship",
+    "upstreams",
+    "dc_overrides",
+];
+
+/// Re-render the given top-level tables from `cfg` and upsert each into the
+/// on-disk file, preserving every untouched section (and its comments).
+pub(super) async fn save_sections_to_disk(
+    config_path: &Path,
+    cfg: &ProxyConfig,
+    sections: &[&str],
+) -> Result<String, ApiFailure> {
+    let mut content = tokio::fs::read_to_string(config_path)
+        .await
+        .map_err(|e| ApiFailure::internal(format!("failed to read config: {}", e)))?;
+
+    for section in sections {
+        let rendered = render_top_level_section(cfg, section)?;
+        content = upsert_toml_table(&content, section, &rendered);
+    }
+
+    write_atomic(config_path.to_path_buf(), content.clone()).await?;
+    Ok(compute_revision(&content))
+}
+
+/// Render one top-level table as `[section]\n...\n` (or `[[upstreams]]` array
+/// of tables) from the typed `cfg`. Serializes via the `toml` crate so the
+/// output matches the canonical format Telemt parses.
+fn render_top_level_section(cfg: &ProxyConfig, section: &str) -> Result<String, ApiFailure> {
+    let value = toml::Value::try_from(cfg)
+        .map_err(|e| ApiFailure::internal(format!("failed to serialize config: {}", e)))?;
+    let table = value
+        .get(section)
+        .ok_or_else(|| ApiFailure::internal(format!("unknown section: {}", section)))?;
+
+    // upstreams is an array-of-tables -> render as [[upstreams]] blocks.
+    if let toml::Value::Array(items) = table {
+        let mut out = String::new();
+        for item in items {
+            out.push_str(&format!("[[{}]]\n", section));
+            out.push_str(&toml::to_string(item).map_err(|e| {
+                ApiFailure::internal(format!("failed to serialize {}: {}", section, e))
+            })?);
+            if !out.ends_with('\n') {
+                out.push('\n');
+            }
+        }
+        return Ok(out);
+    }
+
+    // Serialize the table *inside a wrapper keyed by `section`* so the `toml`
+    // crate emits correctly dotted headers for nested sub-tables, e.g.
+    // `[general]` + `[general.modes]` + `[general.links]`. Serializing the
+    // inner table alone would render bare `[modes]`/`[links]` headers, which
+    // would leak as duplicate top-level tables and break config load.
+    let mut wrapper = toml::value::Table::new();
+    wrapper.insert(section.to_string(), table.clone());
+    let mut out = toml::to_string(&toml::Value::Table(wrapper))
+        .map_err(|e| ApiFailure::internal(format!("failed to serialize {}: {}", section, e)))?;
+    if !out.ends_with('\n') {
+        out.push('\n');
+    }
+    Ok(out)
+}
+
 pub(super) async fn save_access_sections_to_disk(
     config_path: &Path,
     cfg: &ProxyConfig,
@@ -135,6 +221,15 @@ fn render_access_section(cfg: &ProxyConfig, section: AccessSection) -> Result<St
                 .collect();
             serialize_table_body(&rows)?
         }
+        AccessSection::UserEnabled => {
+            let rows: BTreeMap<String, bool> = cfg
+                .access
+                .user_enabled
+                .iter()
+                .map(|(key, value)| (key.clone(), *value))
+                .collect();
+            serialize_table_body(&rows)?
+        }
         AccessSection::UserAdTags => {
             let rows: BTreeMap<String, String> = cfg
                 .access
@@ -204,6 +299,7 @@ fn render_access_section(cfg: &ProxyConfig, section: AccessSection) -> Result<St
 fn access_section_is_empty(cfg: &ProxyConfig, section: AccessSection) -> bool {
     match section {
         AccessSection::Users => cfg.access.users.is_empty(),
+        AccessSection::UserEnabled => cfg.access.user_enabled.is_empty(),
         AccessSection::UserAdTags => cfg.access.user_ad_tags.is_empty(),
         AccessSection::UserMaxTcpConns => cfg.access.user_max_tcp_conns.is_empty(),
         AccessSection::UserExpirations => cfg.access.user_expirations.is_empty(),
@@ -241,11 +337,22 @@ fn serialize_toml_key(key: &str) -> Result<String, ApiFailure> {
 }
 
 fn upsert_toml_table(source: &str, table_name: &str, replacement: &str) -> String {
-    if let Some((start, end)) = find_toml_table_bounds(source, table_name) {
+    let blocks = find_all_table_blocks(source, table_name);
+    if let Some(&(first_start, first_end)) = blocks.first() {
+        // Replace the first block in place and delete any further blocks that
+        // also belong to this table. Telemt writes a section's sub-tables
+        // contiguously, but a hand-edited config may scatter them; dropping the
+        // extras here prevents the duplicate-table corruption that would
+        // otherwise break config load.
         let mut out = String::with_capacity(source.len() + replacement.len());
-        out.push_str(&source[..start]);
+        out.push_str(&source[..first_start]);
         out.push_str(replacement);
-        out.push_str(&source[end..]);
+        let mut cursor = first_end;
+        for &(start, end) in &blocks[1..] {
+            out.push_str(&source[cursor..start]);
+            cursor = end;
+        }
+        out.push_str(&source[cursor..]);
         return out;
     }
 
@@ -260,24 +367,62 @@ fn upsert_toml_table(source: &str, table_name: &str, replacement: &str) -> Strin
     out
 }
 
+/// Whether a (comment-stripped, trimmed) TOML header line belongs to
+/// `table_name`: the table itself (`[X]` / `[[X]]`) or any of its nested
+/// sub-tables (`[X.…]` / `[[X.…]]`). The trailing dot guards against sibling
+/// prefixes — `access.users` must not match `access.user_enabled`.
+fn header_belongs_to(header: &str, table_name: &str) -> bool {
+    let body = match header.strip_prefix("[[").and_then(|h| h.strip_suffix("]]")) {
+        Some(body) => body,
+        None => match header.strip_prefix('[').and_then(|h| h.strip_suffix(']')) {
+            Some(body) => body,
+            None => return false,
+        },
+    };
+    let body = body.trim();
+    body == table_name
+        || body
+            .strip_prefix(table_name)
+            .is_some_and(|rest| rest.starts_with('.'))
+}
+
+/// Locate the first contiguous byte range covering `table_name` and the nested
+/// sub-tables immediately following it. Used for existence checks; see
+/// [`find_all_table_blocks`] for the full set of (possibly scattered) blocks.
 fn find_toml_table_bounds(source: &str, table_name: &str) -> Option<(usize, usize)> {
-    let target = format!("[{}]", table_name);
+    find_all_table_blocks(source, table_name).into_iter().next()
+}
+
+/// Locate every byte range that belongs to `table_name`: the table header and
+/// its nested sub-tables. Returns one range per contiguous run, so a config
+/// where a section's sub-tables are scattered (e.g. hand-edited) yields several
+/// ranges — letting the caller collapse them into a single rendered block.
+fn find_all_table_blocks(source: &str, table_name: &str) -> Vec<(usize, usize)> {
+    let mut blocks = Vec::new();
     let mut offset = 0usize;
-    let mut start = None;
+    let mut start: Option<usize> = None;
 
     for line in source.split_inclusive('\n') {
-        let trimmed = line.trim();
+        // Drop any inline comment so a hand-edited header like
+        // `[censorship] # note` still matches. Section names never contain `#`.
+        let header = line.trim().split('#').next().unwrap_or("").trim();
+        let is_header = header.starts_with('[');
         if let Some(start_offset) = start {
-            if trimmed.starts_with('[') {
-                return Some((start_offset, offset));
+            if is_header && !header_belongs_to(header, table_name) {
+                blocks.push((start_offset, offset));
+                start = None;
             }
-        } else if trimmed == target {
+        }
+        if start.is_none() && header_belongs_to(header, table_name) {
             start = Some(offset);
         }
         offset = offset.saturating_add(line.len());
     }
 
-    start.map(|start_offset| (start_offset, source.len()))
+    if let Some(start_offset) = start {
+        blocks.push((start_offset, source.len()));
+    }
+    blocks
 }
 
 async fn write_atomic(path: PathBuf, contents: String) -> Result<(), ApiFailure> {
@@ -324,6 +469,189 @@ fn write_atomic_sync(path: &Path, contents: &str) -> std::io::Result<()> {
 mod tests {
     use super::*;
 
+    #[tokio::test]
+    async fn save_sections_preserves_other_tables_and_comments() {
+        let dir = std::env::temp_dir().join(format!("cfgtest-{}", rand::random::<u64>()));
+        std::fs::create_dir_all(&dir).unwrap();
+        let path = dir.join("config.toml");
+        std::fs::write(
+            &path,
+            "# top comment\n[censorship]\ntls_domain = \"old.example\"\n\n[server]\nport = 443\n",
+        )
+        .unwrap();
+
+        let mut cfg = ProxyConfig::default();
+        cfg.censorship.tls_domain = "new.example".to_string();
+        cfg.server.port = 443;
+
+        let rev = save_sections_to_disk(&path, &cfg, &["censorship"])
+            .await
+            .unwrap();
+
+        let written = std::fs::read_to_string(&path).unwrap();
+        assert!(written.contains("tls_domain = \"new.example\""));
+        assert!(written.contains("# top comment")); // untouched comment kept
+        assert!(written.contains("[server]\nport = 443")); // untouched table kept
+        assert_eq!(rev, compute_revision(&written));
+        std::fs::remove_dir_all(&dir).ok();
+    }
+
+    #[test]
+    fn find_bounds_matches_array_of_tables() {
+        let src =
+            "[server]\nport = 1\n\n[[upstreams]]\nkind = \"a\"\n\n[[upstreams]]\nkind = \"b\"\n";
+        let bounds = find_toml_table_bounds(src, "upstreams");
+        assert!(bounds.is_some(), "should locate [[upstreams]] block start");
+        let (start, end) = bounds.unwrap();
+        let slice = &src[start..end];
+        assert!(slice.starts_with("[[upstreams]]"));
+        assert!(slice.contains("kind = \"b\"")); // spans through the last upstream block
+    }
+
+    #[test]
+    fn find_bounds_matches_header_with_inline_comment() {
+        let src = "[censorship] # notes\ntls_domain = \"a\"\n\n[server]\nport = 1\n";
+        let bounds = find_toml_table_bounds(src, "censorship");
+        assert!(bounds.is_some(), "commented header must still match");
+        let (start, end) = bounds.unwrap();
+        let slice = &src[start..end];
+        assert!(slice.starts_with("[censorship] # notes"));
+        assert!(slice.contains("tls_domain"));
+        assert!(!slice.contains("[server]")); // terminates at the next header
+    }
+
+    #[tokio::test]
+    async fn save_general_section_keeps_subtables_dotted_without_duplicates() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("config.toml");
+        tokio::fs::write(
+            &path,
+            "[general]\nprefer_ipv6 = false\n\n[general.modes]\ntls = true\n\n\
+             [general.links]\npublic_host = \"old.example\"\n\n[server]\nport = 443\n",
+        )
+        .await
+        .unwrap();
+
+        let mut cfg = ProxyConfig::default();
+        cfg.general.prefer_ipv6 = true;
+
+        save_sections_to_disk(&path, &cfg, &["general"])
+            .await
+            .unwrap();
+
+        let written = tokio::fs::read_to_string(&path).await.unwrap();
+
+        // No bare top-level [modes] / [links] headers leaked.
+        for line in written.lines() {
+            let header = line.trim();
+            assert_ne!(header, "[modes]", "leaked top-level [modes]:\n{written}");
+            assert_ne!(header, "[links]", "leaked top-level [links]:\n{written}");
+        }
+
+        // Sub-tables kept their dotted prefix exactly once each.
+        assert_eq!(
+            written.matches("[general.modes]").count(),
+            1,
+            "[general.modes] must appear exactly once:\n{written}"
+        );
+        assert_eq!(
+            written.matches("[general.links]").count(),
+            1,
+            "[general.links] must appear exactly once:\n{written}"
+        );
+
+        // Result parses (duplicate tables would error here).
+        toml::from_str::<toml::Value>(&written)
+            .unwrap_or_else(|e| panic!("written config must parse: {e}\n{written}"));
+
+        assert!(written.contains("[server]\nport = 443")); // untouched table kept
+    }
+
+    #[tokio::test]
+    async fn save_general_section_is_idempotent_across_repeated_saves() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("config.toml");
+        tokio::fs::write(
+            &path,
+            "[general]\nprefer_ipv6 = false\n\n[general.modes]\ntls = true\n\n\
+             [general.links]\npublic_host = \"old.example\"\n",
+        )
+        .await
+        .unwrap();
+
+        let mut cfg = ProxyConfig::default();
+        cfg.general.prefer_ipv6 = true;
+
+        save_sections_to_disk(&path, &cfg, &["general"])
+            .await
+            .unwrap();
+        save_sections_to_disk(&path, &cfg, &["general"])
+            .await
+            .unwrap();
+
+        let written = tokio::fs::read_to_string(&path).await.unwrap();
+        assert_eq!(written.matches("[general.modes]").count(), 1, "{written}");
+        assert_eq!(written.matches("[general.links]").count(), 1, "{written}");
+        assert_eq!(written.matches("[general]").count(), 1, "{written}");
+        toml::from_str::<toml::Value>(&written)
+            .unwrap_or_else(|e| panic!("written config must parse: {e}\n{written}"));
+    }
+
+    #[test]
+    fn find_bounds_spans_dotted_subtables() {
+        let src = "[general]\nprefer_ipv6 = false\n\n[general.modes]\ntls = true\n\n\
+                   [general.links]\npublic_host = \"a\"\n\n[server]\nport = 1\n";
+        let bounds = find_toml_table_bounds(src, "general");
+        assert!(bounds.is_some(), "should locate [general] block");
+        let (start, end) = bounds.unwrap();
+        let slice = &src[start..end];
+        assert!(slice.starts_with("[general]"));
+        assert!(slice.contains("[general.modes]")); // spans nested sub-tables
+        assert!(slice.contains("[general.links]"));
+        assert!(!slice.contains("[server]")); // terminates at the next unrelated header
+    }
+
+    #[test]
+    fn find_bounds_does_not_overrun_sibling_prefix() {
+        // access.users must not swallow access.user_enabled (dot guards the prefix).
+        let src = "[access.users]\nalice = \"x\"\n\n[access.user_enabled]\nalice = true\n";
+        let bounds = find_toml_table_bounds(src, "access.users").unwrap();
+        let slice = &src[bounds.0..bounds.1];
+        assert!(slice.starts_with("[access.users]"));
+        assert!(!slice.contains("[access.user_enabled]"));
+    }
+
+    #[tokio::test]
+    async fn save_general_handles_non_contiguous_subtables() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("config.toml");
+        // Hand-edited layout: [general.modes] sits AFTER an unrelated [server].
+        tokio::fs::write(
+            &path,
+            "[general]\nprefer_ipv6 = false\n\n[server]\nport = 443\n\n\
+             [general.modes]\ntls = true\n",
+        )
+        .await
+        .unwrap();
+
+        let mut cfg = ProxyConfig::default();
+        cfg.general.prefer_ipv6 = true;
+
+        save_sections_to_disk(&path, &cfg, &["general"])
+            .await
+            .unwrap();
+
+        let written = tokio::fs::read_to_string(&path).await.unwrap();
+        assert_eq!(
+            written.matches("[general.modes]").count(),
+            1,
+            "non-contiguous [general.modes] must not duplicate:\n{written}"
+        );
+        toml::from_str::<toml::Value>(&written)
+            .unwrap_or_else(|e| panic!("written config must parse: {e}\n{written}"));
+        assert!(written.contains("[server]")); // unrelated section preserved
+    }
+
     #[test]
     fn render_user_rate_limits_section() {
         let mut cfg = ProxyConfig::default();

src/api/http_utils.rs

@@ -1,6 +1,7 @@
 use http_body_util::{BodyExt, Full};
 use hyper::StatusCode;
 use hyper::body::{Bytes, Incoming};
+use hyper::header::ALLOW;
 use serde::Serialize;
 use serde::de::DeserializeOwned;
 
@@ -25,6 +26,8 @@ pub(super) fn success_response<T: Serialize>(
 }
 
 pub(super) fn error_response(request_id: u64, failure: ApiFailure) -> hyper::Response<Full<Bytes>> {
+    let status = failure.status;
+    let allow = failure.allow;
     let payload = ErrorResponse {
         ok: false,
         error: ErrorBody {
@@ -40,11 +43,13 @@ pub(super) fn error_response(request_id: u64, failure: ApiFailure) -> hyper::Res
         )
         .into_bytes()
     });
-    hyper::Response::builder()
-        .status(failure.status)
-        .header("content-type", "application/json; charset=utf-8")
-        .body(Full::new(Bytes::from(body)))
-        .unwrap()
+    let mut builder = hyper::Response::builder()
+        .status(status)
+        .header("content-type", "application/json; charset=utf-8");
+    if let Some(allow) = allow {
+        builder = builder.header(ALLOW, allow);
+    }
+    builder.body(Full::new(Bytes::from(body))).unwrap()
 }
 
 pub(super) async fn read_json<T: DeserializeOwned>(

src/api/mod.rs

@@ -22,11 +22,13 @@ use tracing::{debug, info, warn};
 use crate::config::{ApiGrayAction, ProxyConfig};
 use crate::ip_tracker::UserIpTracker;
 use crate::proxy::route_mode::RouteRuntimeController;
+use crate::proxy::shared_state::ProxySharedState;
 use crate::startup::StartupTracker;
 use crate::stats::Stats;
 use crate::transport::UpstreamManager;
 use crate::transport::middle_proxy::MePool;
 
+mod config_edit;
 mod config_store;
 mod events;
 mod http_utils;
@@ -41,7 +43,9 @@ mod runtime_watch;
 mod runtime_zero;
 mod users;
 
-use config_store::{current_revision, load_config_from_disk, parse_if_match};
+use config_store::{
+    current_revision, ensure_expected_revision, load_config_from_disk, parse_if_match,
+};
 use events::ApiEventStore;
 use http_utils::{error_response, read_json, read_optional_json, success_response};
 use model::{
@@ -49,9 +53,10 @@ use model::{
     PatchUserRequest, ResetUserQuotaResponse, RotateSecretRequest, SummaryData, UserActiveIps,
     is_valid_username,
 };
+use patch::Patch;
 use runtime_edge::{
     EdgeConnectionsCacheEntry, build_runtime_connections_summary_data,
-    build_runtime_events_recent_data,
+    build_runtime_events_recent_data, build_runtime_tls_fingerprints_data,
 };
 use runtime_init::build_runtime_initialization_data;
 use runtime_min::{
@@ -69,12 +74,18 @@ use runtime_zero::{
     build_system_info_data,
 };
 use users::{
-    build_user_quota_list, create_user, delete_user, patch_user, rotate_secret, users_from_config,
+    build_user_quota_list, create_user, delete_user, patch_user, rotate_secret, set_user_enabled,
+    users_from_config,
 };
 
 const API_MAX_CONTROL_CONNECTIONS: usize = 1024;
 const API_HTTP_CONNECTION_TIMEOUT: Duration = Duration::from_secs(15);
 const ROUTE_USERNAME_ERROR: &str = "username must match [A-Za-z0-9_.-] and be 1..64 chars";
+const ALLOW_GET: &str = "GET";
+const ALLOW_POST: &str = "POST";
+const ALLOW_GET_POST: &str = "GET, POST";
+const ALLOW_GET_PATCH_DELETE: &str = "GET, PATCH, DELETE";
+const ALLOW_GET_PATCH: &str = "GET, PATCH";
 
 pub(super) struct ApiRuntimeState {
     pub(super) process_started_at_epoch_secs: u64,
@@ -101,6 +112,7 @@ pub(super) struct ApiShared {
     pub(super) runtime_state: Arc<ApiRuntimeState>,
     pub(super) startup_tracker: Arc<StartupTracker>,
     pub(super) route_runtime: Arc<RouteRuntimeController>,
+    pub(super) proxy_shared: Arc<ProxySharedState>,
 }
 
 impl ApiShared {
@@ -125,12 +137,68 @@ fn parse_route_username(user: &str) -> Result<&str, ApiFailure> {
     }
 }
 
+fn user_action_route_matches(path: &str, suffix: &str) -> bool {
+    path.strip_prefix("/v1/users/")
+        .and_then(|path| path.strip_suffix(suffix))
+        .map(|user| !user.is_empty() && !user.contains('/'))
+        .unwrap_or(false)
+}
+
+fn allowed_methods_for_path(path: &str) -> Option<&'static str> {
+    match path {
+        "/v1/health"
+        | "/v1/health/ready"
+        | "/v1/system/info"
+        | "/v1/runtime/gates"
+        | "/v1/runtime/initialization"
+        | "/v1/limits/effective"
+        | "/v1/security/posture"
+        | "/v1/security/whitelist"
+        | "/v1/stats/summary"
+        | "/v1/stats/zero/all"
+        | "/v1/stats/upstreams"
+        | "/v1/stats/minimal/all"
+        | "/v1/stats/me-writers"
+        | "/v1/stats/dcs"
+        | "/v1/runtime/me-pool-state"
+        | "/v1/runtime/me_pool_state"
+        | "/v1/runtime/me-quality"
+        | "/v1/runtime/me_quality"
+        | "/v1/runtime/upstream-quality"
+        | "/v1/runtime/upstream_quality"
+        | "/v1/runtime/nat-stun"
+        | "/v1/runtime/nat_stun"
+        | "/v1/runtime/me-selftest"
+        | "/v1/runtime/connections/summary"
+        | "/v1/runtime/events/recent"
+        | "/v1/runtime/tls-fingerprints"
+        | "/v1/stats/users/active-ips"
+        | "/v1/stats/users/quota"
+        | "/v1/stats/users" => Some(ALLOW_GET),
+        "/v1/users" => Some(ALLOW_GET_POST),
+        "/v1/config" => Some(ALLOW_GET_PATCH),
+        _ if user_action_route_matches(path, "/reset-quota") => Some(ALLOW_POST),
+        _ if user_action_route_matches(path, "/rotate-secret") => Some(ALLOW_POST),
+        _ if user_action_route_matches(path, "/enable") => Some(ALLOW_POST),
+        _ if user_action_route_matches(path, "/disable") => Some(ALLOW_POST),
+        _ if path
+            .strip_prefix("/v1/users/")
+            .map(|user| !user.is_empty() && !user.contains('/'))
+            .unwrap_or(false) =>
+        {
+            Some(ALLOW_GET_PATCH_DELETE)
+        }
+        _ => None,
+    }
+}
+
 pub async fn serve(
     listen: SocketAddr,
     stats: Arc<Stats>,
     ip_tracker: Arc<UserIpTracker>,
     me_pool: Arc<RwLock<Option<Arc<MePool>>>>,
     route_runtime: Arc<RouteRuntimeController>,
+    proxy_shared: Arc<ProxySharedState>,
     upstream_manager: Arc<UpstreamManager>,
     config_rx: watch::Receiver<Arc<ProxyConfig>>,
     admission_rx: watch::Receiver<bool>,
@@ -180,6 +248,7 @@ pub async fn serve(
         runtime_state: runtime_state.clone(),
         startup_tracker,
         route_runtime,
+        proxy_shared,
     });
 
     spawn_runtime_watchers(
@@ -435,22 +504,22 @@ async fn handle(
                 let data = build_dcs_data(shared.as_ref(), api_cfg).await;
                 Ok(success_response(StatusCode::OK, data, revision))
             }
-            ("GET", "/v1/runtime/me_pool_state") => {
+            ("GET", "/v1/runtime/me-pool-state") | ("GET", "/v1/runtime/me_pool_state") => {
                 let revision = current_revision(&shared.config_path).await?;
                 let data = build_runtime_me_pool_state_data(shared.as_ref()).await;
                 Ok(success_response(StatusCode::OK, data, revision))
             }
-            ("GET", "/v1/runtime/me_quality") => {
+            ("GET", "/v1/runtime/me-quality") | ("GET", "/v1/runtime/me_quality") => {
                 let revision = current_revision(&shared.config_path).await?;
                 let data = build_runtime_me_quality_data(shared.as_ref()).await;
                 Ok(success_response(StatusCode::OK, data, revision))
             }
-            ("GET", "/v1/runtime/upstream_quality") => {
+            ("GET", "/v1/runtime/upstream-quality") | ("GET", "/v1/runtime/upstream_quality") => {
                 let revision = current_revision(&shared.config_path).await?;
                 let data = build_runtime_upstream_quality_data(shared.as_ref()).await;
                 Ok(success_response(StatusCode::OK, data, revision))
             }
-            ("GET", "/v1/runtime/nat_stun") => {
+            ("GET", "/v1/runtime/nat-stun") | ("GET", "/v1/runtime/nat_stun") => {
                 let revision = current_revision(&shared.config_path).await?;
                 let data = build_runtime_nat_stun_data(shared.as_ref()).await;
                 Ok(success_response(StatusCode::OK, data, revision))
@@ -475,6 +544,15 @@ async fn handle(
                 );
                 Ok(success_response(StatusCode::OK, data, revision))
             }
+            ("GET", "/v1/runtime/tls-fingerprints") => {
+                let revision = current_revision(&shared.config_path).await?;
+                let data = build_runtime_tls_fingerprints_data(
+                    shared.as_ref(),
+                    cfg.as_ref(),
+                    query.as_deref(),
+                );
+                Ok(success_response(StatusCode::OK, data, revision))
+            }
             ("GET", "/v1/stats/users/active-ips") => {
                 let revision = current_revision(&shared.config_path).await?;
                 let usernames: Vec<_> = cfg.access.users.keys().cloned().collect();
@@ -506,7 +584,7 @@ async fn handle(
                 .await;
                 Ok(success_response(StatusCode::OK, users, revision))
             }
-            ("GET", "/v1/users/quota") => {
+            ("GET", "/v1/stats/users/quota") => {
                 let revision = current_revision(&shared.config_path).await?;
                 let disk_cfg = load_config_from_disk(&shared.config_path).await?;
                 let data = build_user_quota_list(&disk_cfg, shared.stats.as_ref());
@@ -525,6 +603,7 @@ async fn handle(
                 }
                 let expected_revision = parse_if_match(req.headers());
                 let body = read_json::<CreateUserRequest>(req.into_body(), body_limit).await?;
+                let requested_enabled = body.enabled;
                 let result = create_user(body, expected_revision, &shared).await;
                 let (mut data, revision) = match result {
                     Ok(ok) => ok,
@@ -537,6 +616,25 @@ async fn handle(
                 };
                 let runtime_cfg = config_rx.borrow().clone();
                 data.user.in_runtime = runtime_cfg.access.users.contains_key(&data.user.username);
+                if let Some(enabled) = requested_enabled {
+                    shared
+                        .proxy_shared
+                        .set_user_enabled(&data.user.username, enabled);
+                    if !enabled {
+                        let cancelled = shared
+                            .proxy_shared
+                            .cancel_user_sessions(&data.user.username);
+                        if cancelled > 0 {
+                            shared.runtime_events.record(
+                                "api.user.disable.runtime",
+                                format!(
+                                    "username={} cancelled_sessions={}",
+                                    data.user.username, cancelled
+                                ),
+                            );
+                        }
+                    }
+                }
                 shared.runtime_events.record(
                     "api.user.create.ok",
                     format!("username={}", data.user.username),
@@ -548,7 +646,131 @@ async fn handle(
                 };
                 Ok(success_response(status, data, revision))
             }
+            ("GET", "/v1/config") => {
+                let (value, revision) =
+                    config_edit::read_managed_config(&shared.config_path).await?;
+                Ok(success_response(StatusCode::OK, value, revision))
+            }
+            ("PATCH", "/v1/config") => {
+                if api_cfg.read_only {
+                    return Ok(error_response(
+                        request_id,
+                        ApiFailure::new(
+                            StatusCode::FORBIDDEN,
+                            "read_only",
+                            "API runs in read-only mode",
+                        ),
+                    ));
+                }
+                let expected_revision = parse_if_match(req.headers());
+                let body = read_json::<serde_json::Value>(req.into_body(), body_limit).await?;
+                match config_edit::patch_config(body, expected_revision, &shared).await {
+                    Ok(resp) => {
+                        let revision = resp.revision.clone();
+                        Ok(success_response(StatusCode::OK, resp, revision))
+                    }
+                    Err(error) => {
+                        shared
+                            .runtime_events
+                            .record("api.config.patch.failed", error.code);
+                        Err(error)
+                    }
+                }
+            }
             _ => {
+                if method == Method::POST
+                    && let Some(base_user) = normalized_path
+                        .strip_prefix("/v1/users/")
+                        .and_then(|path| path.strip_suffix("/enable"))
+                    && !base_user.is_empty()
+                    && !base_user.contains('/')
+                {
+                    let base_user = parse_route_username(base_user)?;
+                    if api_cfg.read_only {
+                        return Ok(error_response(
+                            request_id,
+                            ApiFailure::new(
+                                StatusCode::FORBIDDEN,
+                                "read_only",
+                                "API runs in read-only mode",
+                            ),
+                        ));
+                    }
+                    let expected_revision = parse_if_match(req.headers());
+                    let result =
+                        set_user_enabled(base_user, true, expected_revision, &shared).await;
+                    let (mut data, revision) = match result {
+                        Ok(ok) => ok,
+                        Err(error) => {
+                            shared.runtime_events.record(
+                                "api.user.enable.failed",
+                                format!("username={} code={}", base_user, error.code),
+                            );
+                            return Err(error);
+                        }
+                    };
+                    let runtime_cfg = config_rx.borrow().clone();
+                    data.in_runtime = runtime_cfg.access.users.contains_key(&data.username);
+                    shared.proxy_shared.set_user_enabled(base_user, true);
+                    shared
+                        .runtime_events
+                        .record("api.user.enable.ok", format!("username={}", base_user));
+                    let status = if data.in_runtime {
+                        StatusCode::OK
+                    } else {
+                        StatusCode::ACCEPTED
+                    };
+                    return Ok(success_response(status, data, revision));
+                }
+                if method == Method::POST
+                    && let Some(base_user) = normalized_path
+                        .strip_prefix("/v1/users/")
+                        .and_then(|path| path.strip_suffix("/disable"))
+                    && !base_user.is_empty()
+                    && !base_user.contains('/')
+                {
+                    let base_user = parse_route_username(base_user)?;
+                    if api_cfg.read_only {
+                        return Ok(error_response(
+                            request_id,
+                            ApiFailure::new(
+                                StatusCode::FORBIDDEN,
+                                "read_only",
+                                "API runs in read-only mode",
+                            ),
+                        ));
+                    }
+                    let expected_revision = parse_if_match(req.headers());
+                    let result =
+                        set_user_enabled(base_user, false, expected_revision, &shared).await;
+                    let (mut data, revision) = match result {
+                        Ok(ok) => ok,
+                        Err(error) => {
+                            shared.runtime_events.record(
+                                "api.user.disable.failed",
+                                format!("username={} code={}", base_user, error.code),
+                            );
+                            return Err(error);
+                        }
+                    };
+                    let runtime_cfg = config_rx.borrow().clone();
+                    data.in_runtime = runtime_cfg.access.users.contains_key(&data.username);
+                    let newly_disabled = shared.proxy_shared.set_user_enabled(base_user, false);
+                    let cancelled = shared.proxy_shared.cancel_user_sessions(base_user);
+                    shared.runtime_events.record(
+                        "api.user.disable.ok",
+                        format!(
+                            "username={} newly_disabled={} cancelled_sessions={}",
+                            base_user, newly_disabled, cancelled
+                        ),
+                    );
+                    let status = if data.in_runtime {
+                        StatusCode::OK
+                    } else {
+                        StatusCode::ACCEPTED
+                    };
+                    return Ok(success_response(status, data, revision));
+                }
                 if method == Method::POST
                     && let Some(user) = normalized_path
                         .strip_prefix("/v1/users/")
@@ -567,6 +789,16 @@ async fn handle(
                             ),
                         ));
                     }
+                    let expected_revision = parse_if_match(req.headers());
+                    let disk_cfg = load_config_from_disk(&shared.config_path).await?;
+                    ensure_expected_revision(&shared.config_path, expected_revision.as_deref())
+                        .await?;
+                    if !disk_cfg.access.users.contains_key(user) {
+                        return Ok(error_response(
+                            request_id,
+                            ApiFailure::new(StatusCode::NOT_FOUND, "not_found", "User not found"),
+                        ));
+                    }
                     let snapshot = match crate::quota_state::reset_user_quota(
                         &shared.quota_state_path,
                         shared.stats.as_ref(),
@@ -696,6 +928,11 @@ async fn handle(
                         let expected_revision = parse_if_match(req.headers());
                         let body =
                             read_json::<PatchUserRequest>(req.into_body(), body_limit).await?;
+                        let enabled_update = match &body.enabled {
+                            Patch::Unchanged => None,
+                            Patch::Remove => Some(true),
+                            Patch::Set(enabled) => Some(*enabled),
+                        };
                         let result = patch_user(user, body, expected_revision, &shared).await;
                         let (mut data, revision) = match result {
                             Ok(ok) => ok,
@@ -709,6 +946,22 @@ async fn handle(
                         };
                         let runtime_cfg = config_rx.borrow().clone();
                         data.in_runtime = runtime_cfg.access.users.contains_key(&data.username);
+                        if let Some(enabled) = enabled_update {
+                            shared
+                                .proxy_shared
+                                .set_user_enabled(&data.username, enabled);
+                            if !enabled {
+                                let cancelled =
+                                    shared.proxy_shared.cancel_user_sessions(&data.username);
+                                shared.runtime_events.record(
+                                    "api.user.disable.runtime",
+                                    format!(
+                                        "username={} cancelled_sessions={}",
+                                        data.username, cancelled
+                                    ),
+                                );
+                            }
+                        }
                         shared
                             .runtime_events
                             .record("api.user.patch.ok", format!("username={}", data.username));
@@ -742,9 +995,12 @@ async fn handle(
                                 return Err(error);
                             }
                         };
-                        shared
-                            .runtime_events
-                            .record("api.user.delete.ok", format!("username={}", deleted_user));
+                        shared.proxy_shared.set_user_enabled(&deleted_user, true);
+                        let cancelled = shared.proxy_shared.cancel_user_sessions(&deleted_user);
+                        shared.runtime_events.record(
+                            "api.user.delete.ok",
+                            format!("username={} cancelled_sessions={}", deleted_user, cancelled),
+                        );
                         let runtime_cfg = config_rx.borrow().clone();
                         let in_runtime = runtime_cfg.access.users.contains_key(&deleted_user);
                         let response = DeleteUserResponse {
@@ -761,16 +1017,18 @@ async fn handle(
                     if method == Method::POST {
                         return Ok(error_response(
                             request_id,
-                            ApiFailure::new(StatusCode::NOT_FOUND, "not_found", "Route not found"),
+                            ApiFailure::method_not_allowed(ALLOW_GET_PATCH_DELETE),
                         ));
                     }
                     return Ok(error_response(
                         request_id,
-                        ApiFailure::new(
-                            StatusCode::METHOD_NOT_ALLOWED,
-                            "method_not_allowed",
-                            "Unsupported HTTP method for this route",
-                        ),
+                        ApiFailure::method_not_allowed(ALLOW_GET_PATCH_DELETE),
+                    ));
+                }
+                if let Some(allow) = allowed_methods_for_path(normalized_path) {
+                    return Ok(error_response(
+                        request_id,
+                        ApiFailure::method_not_allowed(allow),
                     ));
                 }
                 debug!(

src/api/model.rs

@@ -15,6 +15,7 @@ pub(super) struct ApiFailure {
     pub(super) status: StatusCode,
     pub(super) code: &'static str,
     pub(super) message: String,
+    pub(super) allow: Option<&'static str>,
 }
 
 impl ApiFailure {
@@ -23,6 +24,7 @@ impl ApiFailure {
             status,
             code,
             message: message.into(),
+            allow: None,
         }
     }
 
@@ -33,6 +35,15 @@ impl ApiFailure {
     pub(super) fn bad_request(message: impl Into<String>) -> Self {
         Self::new(StatusCode::BAD_REQUEST, "bad_request", message)
     }
+
+    pub(super) fn method_not_allowed(allow: &'static str) -> Self {
+        Self {
+            status: StatusCode::METHOD_NOT_ALLOWED,
+            code: "method_not_allowed",
+            message: "Unsupported HTTP method for this route".to_string(),
+            allow: Some(allow),
+        }
+    }
 }
 
 #[derive(Serialize)]
@@ -468,6 +479,7 @@ pub(super) struct TlsDomainLink {
 #[derive(Serialize)]
 pub(super) struct UserInfo {
     pub(super) username: String,
+    pub(super) enabled: bool,
     pub(super) in_runtime: bool,
     pub(super) user_ad_tag: Option<String>,
     pub(super) max_tcp_conns: Option<usize>,
@@ -534,6 +546,7 @@ pub(super) struct CreateUserRequest {
     pub(super) rate_limit_up_bps: Option<u64>,
     pub(super) rate_limit_down_bps: Option<u64>,
     pub(super) max_unique_ips: Option<usize>,
+    pub(super) enabled: Option<bool>,
 }
 
 #[derive(Deserialize)]
@@ -553,6 +566,8 @@ pub(super) struct PatchUserRequest {
     pub(super) rate_limit_down_bps: Patch<u64>,
     #[serde(default, deserialize_with = "patch_field")]
     pub(super) max_unique_ips: Patch<usize>,
+    #[serde(default, deserialize_with = "patch_field")]
+    pub(super) enabled: Patch<bool>,
 }
 
 #[derive(Default, Deserialize)]

src/api/runtime_edge.rs

@@ -12,6 +12,8 @@ const FEATURE_DISABLED_REASON: &str = "feature_disabled";
 const SOURCE_UNAVAILABLE_REASON: &str = "source_unavailable";
 const EVENTS_DEFAULT_LIMIT: usize = 50;
 const EVENTS_MAX_LIMIT: usize = 1000;
+const TLS_FINGERPRINTS_MAX_LIMIT: usize = 1000;
+const RUNTIME_EDGE_RETENTION_MAX_MINUTES: u64 = 24 * 60;
 
 #[derive(Clone, Serialize)]
 pub(super) struct RuntimeEdgeConnectionUserData {
@@ -90,6 +92,44 @@ pub(super) struct RuntimeEdgeEventsData {
     pub(super) data: Option<RuntimeEdgeEventsPayload>,
 }
 
+#[derive(Serialize)]
+pub(super) struct RuntimeEdgeTlsFingerprintRow {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub(super) scope: Option<String>,
+    pub(super) ja3: String,
+    pub(super) ja3_raw: String,
+    pub(super) ja4: String,
+    pub(super) ja4_raw: String,
+    pub(super) total: u64,
+    pub(super) auth_success: u64,
+    pub(super) bad_or_probe: u64,
+    pub(super) first_seen_epoch_secs: u64,
+    pub(super) last_seen_epoch_secs: u64,
+}
+
+#[derive(Serialize)]
+pub(super) struct RuntimeEdgeTlsFingerprintsPayload {
+    pub(super) limit: usize,
+    pub(super) retention_secs: u64,
+    pub(super) capacity: usize,
+    pub(super) dropped_total: u64,
+    pub(super) parse_error_total: u64,
+    pub(super) by_fingerprint: Vec<RuntimeEdgeTlsFingerprintRow>,
+    pub(super) by_ip: Vec<RuntimeEdgeTlsFingerprintRow>,
+    pub(super) by_cidr: Vec<RuntimeEdgeTlsFingerprintRow>,
+    pub(super) by_user: Vec<RuntimeEdgeTlsFingerprintRow>,
+}
+
+#[derive(Serialize)]
+pub(super) struct RuntimeEdgeTlsFingerprintsData {
+    pub(super) enabled: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub(super) reason: Option<&'static str>,
+    pub(super) generated_at_epoch_secs: u64,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub(super) data: Option<RuntimeEdgeTlsFingerprintsPayload>,
+}
+
 pub(super) async fn build_runtime_connections_summary_data(
     shared: &ApiShared,
     cfg: &ProxyConfig,
@@ -162,6 +202,65 @@ pub(super) fn build_runtime_events_recent_data(
     }
 }
 
+pub(super) fn build_runtime_tls_fingerprints_data(
+    shared: &ApiShared,
+    cfg: &ProxyConfig,
+    query: Option<&str>,
+) -> RuntimeEdgeTlsFingerprintsData {
+    let now_epoch_secs = now_epoch_secs();
+    let api_cfg = &cfg.server.api;
+    if !api_cfg.runtime_edge_enabled {
+        return RuntimeEdgeTlsFingerprintsData {
+            enabled: false,
+            reason: Some(FEATURE_DISABLED_REASON),
+            generated_at_epoch_secs: now_epoch_secs,
+            data: None,
+        };
+    }
+
+    let limit = parse_recent_events_limit(
+        query,
+        api_cfg.runtime_edge_top_n.max(1),
+        TLS_FINGERPRINTS_MAX_LIMIT,
+    );
+    let snapshot = shared
+        .stats
+        .tls_fingerprint_snapshot(runtime_edge_retention(cfg), limit);
+
+    RuntimeEdgeTlsFingerprintsData {
+        enabled: true,
+        reason: None,
+        generated_at_epoch_secs: now_epoch_secs,
+        data: Some(RuntimeEdgeTlsFingerprintsPayload {
+            limit,
+            retention_secs: snapshot.retention_secs,
+            capacity: snapshot.capacity,
+            dropped_total: snapshot.dropped_total,
+            parse_error_total: snapshot.parse_error_total,
+            by_fingerprint: snapshot
+                .by_fingerprint
+                .into_iter()
+                .map(runtime_tls_fingerprint_row)
+                .collect(),
+            by_ip: snapshot
+                .by_ip
+                .into_iter()
+                .map(runtime_tls_fingerprint_row)
+                .collect(),
+            by_cidr: snapshot
+                .by_cidr
+                .into_iter()
+                .map(runtime_tls_fingerprint_row)
+                .collect(),
+            by_user: snapshot
+                .by_user
+                .into_iter()
+                .map(runtime_tls_fingerprint_row)
+                .collect(),
+        }),
+    }
+}
+
 async fn get_connections_payload_cached(
     shared: &ApiShared,
     cache_ttl_ms: u64,
@@ -286,6 +385,35 @@ fn parse_recent_events_limit(query: Option<&str>, default_limit: usize, max_limi
     default_limit
 }
 
+fn runtime_edge_retention(cfg: &ProxyConfig) -> Duration {
+    let minutes = cfg
+        .general
+        .beobachten_minutes
+        .clamp(1, RUNTIME_EDGE_RETENTION_MAX_MINUTES);
+    Duration::from_secs(minutes.saturating_mul(60))
+}
+
+fn runtime_tls_fingerprint_row(
+    row: crate::stats::TlsFingerprintSnapshotRow,
+) -> RuntimeEdgeTlsFingerprintRow {
+    RuntimeEdgeTlsFingerprintRow {
+        scope: if row.scope_key.is_empty() {
+            None
+        } else {
+            Some(row.scope_key)
+        },
+        ja3: row.ja3,
+        ja3_raw: row.ja3_raw,
+        ja4: row.ja4,
+        ja4_raw: row.ja4_raw,
+        total: row.total,
+        auth_success: row.auth_success,
+        bad_or_probe: row.bad_or_probe,
+        first_seen_epoch_secs: row.first_seen_epoch_secs,
+        last_seen_epoch_secs: row.last_seen_epoch_secs,
+    }
+}
+
 fn now_epoch_secs() -> u64 {
     SystemTime::now()
         .duration_since(UNIX_EPOCH)

src/api/users.rs

@@ -32,6 +32,7 @@ pub(super) async fn create_user(
     let touches_user_rate_limits =
         body.rate_limit_up_bps.is_some() || body.rate_limit_down_bps.is_some();
     let touches_user_max_unique_ips = body.max_unique_ips.is_some();
+    let touches_user_enabled = matches!(body.enabled, Some(false));
 
     if !is_valid_username(&body.username) {
         return Err(ApiFailure::bad_request(
@@ -111,6 +112,9 @@ pub(super) async fn create_user(
             .user_max_unique_ips
             .insert(body.username.clone(), limit);
     }
+    if matches!(body.enabled, Some(false)) {
+        cfg.access.user_enabled.insert(body.username.clone(), false);
+    }
 
     cfg.validate()
         .map_err(|e| ApiFailure::bad_request(format!("config validation failed: {}", e)))?;
@@ -134,6 +138,9 @@ pub(super) async fn create_user(
     if touches_user_max_unique_ips {
         touched_sections.push(AccessSection::UserMaxUniqueIps);
     }
+    if touches_user_enabled {
+        touched_sections.push(AccessSection::UserEnabled);
+    }
 
     let revision =
         save_access_sections_to_disk(&shared.config_path, &cfg, &touched_sections).await?;
@@ -161,6 +168,7 @@ pub(super) async fn create_user(
         .find(|entry| entry.username == body.username)
         .unwrap_or(UserInfo {
             username: body.username.clone(),
+            enabled: cfg.access.is_user_enabled(&body.username),
             in_runtime: false,
             user_ad_tag: None,
             max_tcp_conns: cfg
@@ -202,6 +210,7 @@ pub(super) async fn patch_user(
     let touches_user_rate_limits = !matches!(&body.rate_limit_up_bps, Patch::Unchanged)
         || !matches!(&body.rate_limit_down_bps, Patch::Unchanged);
     let touches_user_max_unique_ips = !matches!(&body.max_unique_ips, Patch::Unchanged);
+    let touches_user_enabled = !matches!(&body.enabled, Patch::Unchanged);
 
     if let Some(secret) = body.secret.as_ref()
         && !is_valid_user_secret(secret)
@@ -313,6 +322,15 @@ pub(super) async fn patch_user(
             Some(Some(limit))
         }
     };
+    match body.enabled {
+        Patch::Unchanged => {}
+        Patch::Remove | Patch::Set(true) => {
+            cfg.access.user_enabled.remove(user);
+        }
+        Patch::Set(false) => {
+            cfg.access.user_enabled.insert(user.to_string(), false);
+        }
+    }
 
     cfg.validate()
         .map_err(|e| ApiFailure::bad_request(format!("config validation failed: {}", e)))?;
@@ -339,6 +357,9 @@ pub(super) async fn patch_user(
     if touches_user_max_unique_ips {
         touched_sections.push(AccessSection::UserMaxUniqueIps);
     }
+    if touches_user_enabled {
+        touched_sections.push(AccessSection::UserEnabled);
+    }
 
     let revision = if touched_sections.is_empty() {
         current_revision(&shared.config_path).await?
@@ -399,6 +420,7 @@ pub(super) async fn rotate_secret(
         .map_err(|e| ApiFailure::bad_request(format!("config validation failed: {}", e)))?;
     let touched_sections = [
         AccessSection::Users,
+        AccessSection::UserEnabled,
         AccessSection::UserAdTags,
         AccessSection::UserMaxTcpConns,
         AccessSection::UserExpirations,
@@ -434,6 +456,55 @@ pub(super) async fn rotate_secret(
     ))
 }
 
+pub(super) async fn set_user_enabled(
+    user: &str,
+    enabled: bool,
+    expected_revision: Option<String>,
+    shared: &ApiShared,
+) -> Result<(UserInfo, String), ApiFailure> {
+    let _guard = shared.mutation_lock.lock().await;
+    let mut cfg = load_config_from_disk(&shared.config_path).await?;
+    ensure_expected_revision(&shared.config_path, expected_revision.as_deref()).await?;
+
+    if !cfg.access.users.contains_key(user) {
+        return Err(ApiFailure::new(
+            StatusCode::NOT_FOUND,
+            "not_found",
+            "User not found",
+        ));
+    }
+
+    if enabled {
+        cfg.access.user_enabled.remove(user);
+    } else {
+        cfg.access.user_enabled.insert(user.to_string(), false);
+    }
+
+    cfg.validate()
+        .map_err(|e| ApiFailure::bad_request(format!("config validation failed: {}", e)))?;
+    let revision =
+        save_access_sections_to_disk(&shared.config_path, &cfg, &[AccessSection::UserEnabled])
+            .await?;
+    drop(_guard);
+
+    let (detected_ip_v4, detected_ip_v6) = shared.detected_link_ips();
+    let users = users_from_config(
+        &cfg,
+        &shared.stats,
+        &shared.ip_tracker,
+        detected_ip_v4,
+        detected_ip_v6,
+        None,
+    )
+    .await;
+    let user_info = users
+        .into_iter()
+        .find(|entry| entry.username == user)
+        .ok_or_else(|| ApiFailure::internal("failed to build updated user view"))?;
+
+    Ok((user_info, revision))
+}
+
 pub(super) async fn delete_user(
     user: &str,
     expected_revision: Option<String>,
@@ -459,6 +530,7 @@ pub(super) async fn delete_user(
     }
 
     cfg.access.users.remove(user);
+    cfg.access.user_enabled.remove(user);
     cfg.access.user_ad_tags.remove(user);
     cfg.access.user_max_tcp_conns.remove(user);
     cfg.access.user_expirations.remove(user);
@@ -470,6 +542,7 @@ pub(super) async fn delete_user(
         .map_err(|e| ApiFailure::bad_request(format!("config validation failed: {}", e)))?;
     let touched_sections = [
         AccessSection::Users,
+        AccessSection::UserEnabled,
         AccessSection::UserAdTags,
         AccessSection::UserMaxTcpConns,
         AccessSection::UserExpirations,
@@ -518,6 +591,7 @@ pub(super) async fn users_from_config(
             })
             .unwrap_or_else(empty_user_links);
         users.push(UserInfo {
+            enabled: cfg.access.is_user_enabled(&username),
             in_runtime: runtime_cfg
                 .map(|runtime| runtime.access.users.contains_key(&username))
                 .unwrap_or(false),
@@ -876,6 +950,43 @@ mod tests {
         assert_eq!(alice.rate_limit_down_bps, None);
     }
 
+    #[tokio::test]
+    async fn users_from_config_reports_user_enabled_default_and_override() {
+        let mut cfg = ProxyConfig::default();
+        cfg.access.users.insert(
+            "alice".to_string(),
+            "0123456789abcdef0123456789abcdef".to_string(),
+        );
+        cfg.access.users.insert(
+            "bob".to_string(),
+            "fedcba9876543210fedcba9876543210".to_string(),
+        );
+        cfg.access.user_enabled.insert("bob".to_string(), false);
+
+        let stats = Stats::new();
+        let tracker = UserIpTracker::new();
+        let users = users_from_config(&cfg, &stats, &tracker, None, None, None).await;
+        let alice = users
+            .iter()
+            .find(|entry| entry.username == "alice")
+            .expect("alice must be present");
+        let bob = users
+            .iter()
+            .find(|entry| entry.username == "bob")
+            .expect("bob must be present");
+
+        assert!(alice.enabled);
+        assert!(!bob.enabled);
+
+        cfg.access.user_enabled.insert("bob".to_string(), true);
+        let users = users_from_config(&cfg, &stats, &tracker, None, None, None).await;
+        let bob = users
+            .iter()
+            .find(|entry| entry.username == "bob")
+            .expect("bob must be present");
+        assert!(bob.enabled);
+    }
+
     #[tokio::test]
     async fn users_from_config_marks_runtime_membership_when_snapshot_is_provided() {
         let mut disk_cfg = ProxyConfig::default();

src/cli.rs

@@ -705,6 +705,9 @@ ignore_time_skew = false
 type = "direct"
 enabled = true
 weight = 10
+# Optional per-upstream DC family policy:
+# ipv6 = true
+# prefer = 6
 "#,
         username = username,
         secret = secret,

src/config/defaults.rs

@@ -54,6 +54,9 @@ const DEFAULT_CONNTRACK_CONTROL_ENABLED: bool = true;
 const DEFAULT_CONNTRACK_PRESSURE_HIGH_WATERMARK_PCT: u8 = 85;
 const DEFAULT_CONNTRACK_PRESSURE_LOW_WATERMARK_PCT: u8 = 70;
 const DEFAULT_CONNTRACK_DELETE_BUDGET_PER_SEC: u64 = 4096;
+const DEFAULT_SYNLIMIT_SECONDS: u32 = 1;
+const DEFAULT_SYNLIMIT_HITCOUNT: u32 = 1;
+const DEFAULT_SYNLIMIT_BURST: u32 = 2;
 const DEFAULT_UPSTREAM_CONNECT_RETRY_ATTEMPTS: u32 = 2;
 const DEFAULT_UPSTREAM_UNHEALTHY_FAIL_THRESHOLD: u32 = 5;
 const DEFAULT_UPSTREAM_CONNECT_BUDGET_MS: u64 = 3000;
@@ -243,6 +246,18 @@ pub(crate) fn default_conntrack_delete_budget_per_sec() -> u64 {
     DEFAULT_CONNTRACK_DELETE_BUDGET_PER_SEC
 }
 
+pub(crate) fn default_synlimit_seconds() -> u32 {
+    DEFAULT_SYNLIMIT_SECONDS
+}
+
+pub(crate) fn default_synlimit_hitcount() -> u32 {
+    DEFAULT_SYNLIMIT_HITCOUNT
+}
+
+pub(crate) fn default_synlimit_burst() -> u32 {
+    DEFAULT_SYNLIMIT_BURST
+}
+
 pub(crate) fn default_prefer_4() -> u8 {
     4
 }

src/config/hot_reload.rs

@@ -16,10 +16,12 @@
 //! | `general` | `telemetry` / `me_*_policy`    | Applied immediately                            |
 //! | `network` | `dns_overrides`                | Applied immediately                            |
 //! | `access`  | All user/quota fields          | Effective immediately                          |
+//! | `server.listeners` | `synlimit*` for existing endpoints | Netfilter rules reconciled immediately |
 //!
 //! Fields that require re-binding sockets (`server.listeners`, legacy
 //! `server.port`, `censorship.*`, `network.*`, `use_middle_proxy`) are **not**
-//! applied; a warning is emitted.
+//! applied, except for SYN limiter fields on unchanged listener endpoints; a
+//! warning is emitted.
 //! Non-hot changes are never mixed into the runtime config snapshot.
 
 use std::collections::BTreeSet;
@@ -34,7 +36,8 @@ use tracing::{error, info, warn};
 
 use super::load::{LoadedConfig, ProxyConfig};
 use crate::config::{
-    LogLevel, MeBindStaleMode, MeFloorMode, MeSocksKdfPolicy, MeTelemetryLevel, MeWriterPickMode,
+    ListenerConfig, LogLevel, MeBindStaleMode, MeFloorMode, MeSocksKdfPolicy, MeTelemetryLevel,
+    MeWriterPickMode, SynLimitMode,
 };
 
 const HOT_RELOAD_DEBOUNCE: Duration = Duration::from_millis(50);
@@ -118,6 +121,7 @@ pub struct HotFields {
     pub me_admission_poll_ms: u64,
     pub me_warn_rate_limit_ms: u64,
     pub users: std::collections::HashMap<String, String>,
+    pub user_enabled: std::collections::HashMap<String, bool>,
     pub user_ad_tags: std::collections::HashMap<String, String>,
     pub user_max_tcp_conns: std::collections::HashMap<String, usize>,
     pub user_max_tcp_conns_global_each: usize,
@@ -130,6 +134,17 @@ pub struct HotFields {
     pub user_max_unique_ips_global_each: usize,
     pub user_max_unique_ips_mode: crate::config::UserMaxUniqueIpsMode,
     pub user_max_unique_ips_window_secs: u64,
+    pub listener_synlimit: Vec<ListenerSynLimitHotFields>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ListenerSynLimitHotFields {
+    pub ip: IpAddr,
+    pub port: Option<u16>,
+    pub synlimit: SynLimitMode,
+    pub synlimit_seconds: u32,
+    pub synlimit_hitcount: u32,
+    pub synlimit_burst: u32,
 }
 
 impl HotFields {
@@ -247,6 +262,7 @@ impl HotFields {
             me_admission_poll_ms: cfg.general.me_admission_poll_ms,
             me_warn_rate_limit_ms: cfg.general.me_warn_rate_limit_ms,
             users: cfg.access.users.clone(),
+            user_enabled: cfg.access.user_enabled.clone(),
             user_ad_tags: cfg.access.user_ad_tags.clone(),
             user_max_tcp_conns: cfg.access.user_max_tcp_conns.clone(),
             user_max_tcp_conns_global_each: cfg.access.user_max_tcp_conns_global_each,
@@ -258,6 +274,25 @@ impl HotFields {
             user_max_unique_ips_global_each: cfg.access.user_max_unique_ips_global_each,
             user_max_unique_ips_mode: cfg.access.user_max_unique_ips_mode,
             user_max_unique_ips_window_secs: cfg.access.user_max_unique_ips_window_secs,
+            listener_synlimit: cfg
+                .server
+                .listeners
+                .iter()
+                .map(ListenerSynLimitHotFields::from_listener)
+                .collect(),
+        }
+    }
+}
+
+impl ListenerSynLimitHotFields {
+    fn from_listener(listener: &ListenerConfig) -> Self {
+        Self {
+            ip: listener.ip,
+            port: listener.port,
+            synlimit: listener.synlimit,
+            synlimit_seconds: listener.synlimit_seconds,
+            synlimit_hitcount: listener.synlimit_hitcount,
+            synlimit_burst: listener.synlimit_burst,
         }
     }
 }
@@ -310,6 +345,7 @@ fn listeners_equal(
     lhs.iter().zip(rhs.iter()).all(|(a, b)| {
         a.ip == b.ip
             && a.port == b.port
+            && a.client_mss == b.client_mss
             && a.announce == b.announce
             && a.announce_ip == b.announce_ip
             && a.proxy_protocol == b.proxy_protocol
@@ -551,6 +587,7 @@ fn overlay_hot_fields(old: &ProxyConfig, new: &ProxyConfig) -> ProxyConfig {
     cfg.general.me_warn_rate_limit_ms = new.general.me_warn_rate_limit_ms;
 
     cfg.access.users = new.access.users.clone();
+    cfg.access.user_enabled = new.access.user_enabled.clone();
     cfg.access.user_ad_tags = new.access.user_ad_tags.clone();
     cfg.access.user_max_tcp_conns = new.access.user_max_tcp_conns.clone();
     cfg.access.user_max_tcp_conns_global_each = new.access.user_max_tcp_conns_global_each;
@@ -562,6 +599,7 @@ fn overlay_hot_fields(old: &ProxyConfig, new: &ProxyConfig) -> ProxyConfig {
     cfg.access.user_max_unique_ips_global_each = new.access.user_max_unique_ips_global_each;
     cfg.access.user_max_unique_ips_mode = new.access.user_max_unique_ips_mode;
     cfg.access.user_max_unique_ips_window_secs = new.access.user_max_unique_ips_window_secs;
+    overlay_listener_synlimit_fields(&mut cfg.server.listeners, &new.server.listeners);
 
     if cfg.rebuild_runtime_user_auth().is_err() {
         cfg.runtime_user_auth = None;
@@ -570,6 +608,21 @@ fn overlay_hot_fields(old: &ProxyConfig, new: &ProxyConfig) -> ProxyConfig {
     cfg
 }
 
+fn overlay_listener_synlimit_fields(old: &mut [ListenerConfig], new: &[ListenerConfig]) {
+    if old.len() != new.len() {
+        return;
+    }
+    for (old_listener, new_listener) in old.iter_mut().zip(new.iter()) {
+        if old_listener.ip != new_listener.ip || old_listener.port != new_listener.port {
+            continue;
+        }
+        old_listener.synlimit = new_listener.synlimit;
+        old_listener.synlimit_seconds = new_listener.synlimit_seconds;
+        old_listener.synlimit_hitcount = new_listener.synlimit_hitcount;
+        old_listener.synlimit_burst = new_listener.synlimit_burst;
+    }
+}
+
 /// Warn if any non-hot fields changed (require restart).
 fn warn_non_hot_changes(old: &ProxyConfig, new: &ProxyConfig, non_hot_changed: bool) {
     let mut warned = false;
@@ -605,6 +658,7 @@ fn warn_non_hot_changes(old: &ProxyConfig, new: &ProxyConfig, non_hot_changed: b
         || old.server.listen_addr_ipv4 != new.server.listen_addr_ipv4
         || old.server.listen_addr_ipv6 != new.server.listen_addr_ipv6
         || old.server.listen_tcp != new.server.listen_tcp
+        || old.server.client_mss != new.server.client_mss
         || old.server.listen_unix_sock != new.server.listen_unix_sock
         || old.server.listen_unix_sock_perm != new.server.listen_unix_sock_perm
     {
@@ -615,6 +669,7 @@ fn warn_non_hot_changes(old: &ProxyConfig, new: &ProxyConfig, non_hot_changed: b
         || old.censorship.tls_domains != new.censorship.tls_domains
         || old.censorship.tls_fetch_scope != new.censorship.tls_fetch_scope
         || old.censorship.mask != new.censorship.mask
+        || old.censorship.mask_dynamic != new.censorship.mask_dynamic
         || old.censorship.mask_host != new.censorship.mask_host
         || old.censorship.mask_port != new.censorship.mask_port
         || old.censorship.exclusive_mask != new.censorship.exclusive_mask
@@ -844,6 +899,13 @@ fn log_changes(
         );
     }
 
+    if old_hot.listener_synlimit != new_hot.listener_synlimit {
+        info!(
+            "config reload: server.listeners SYN limiter updated ({} listeners)",
+            new_hot.listener_synlimit.len()
+        );
+    }
+
     if old_hot.desync_all_full != new_hot.desync_all_full {
         info!(
             "config reload: desync_all_full: {} → {}",
@@ -1178,6 +1240,16 @@ fn log_changes(
         }
     }
 
+    if old_hot.user_enabled != new_hot.user_enabled {
+        info!(
+            "config reload: user_enabled updated ({} disabled overrides)",
+            new_hot
+                .user_enabled
+                .values()
+                .filter(|enabled| !**enabled)
+                .count()
+        );
+    }
     if old_hot.user_max_tcp_conns != new_hot.user_max_tcp_conns {
         info!(
             "config reload: user_max_tcp_conns updated ({} entries)",
@@ -1474,6 +1546,48 @@ pub fn spawn_config_watcher(
     (config_rx, log_rx)
 }
 
+// ── Change classification ─────────────────────────────────────────────────────
+
+/// Which top-level config sections changed and whether any require a restart.
+#[derive(Debug, Default, Clone, serde::Serialize)]
+pub struct ChangeClassification {
+    pub changed: Vec<String>,
+    pub restart_required: bool,
+}
+
+/// Classify old->new using Telemt's OWN reload rule: overlay the hot fields and
+/// see if anything non-hot remains different. This guarantees `restart_required`
+/// matches actual runtime behavior and never drifts as new fields are added.
+pub fn classify_config_changes(old: &ProxyConfig, new: &ProxyConfig) -> ChangeClassification {
+    let applied = overlay_hot_fields(old, new);
+    let restart_required = !config_equal(&applied, new);
+    ChangeClassification {
+        changed: changed_sections(old, new),
+        restart_required,
+    }
+}
+
+/// Top-level config sections whose canonical serialized form differs between
+/// old and new. Uses the same serialize+canonicalize path as `config_equal`.
+fn changed_sections(old: &ProxyConfig, new: &ProxyConfig) -> Vec<String> {
+    let mut lhs = serde_json::to_value(old).unwrap_or(serde_json::Value::Null);
+    let mut rhs = serde_json::to_value(new).unwrap_or(serde_json::Value::Null);
+    canonicalize_json(&mut lhs);
+    canonicalize_json(&mut rhs);
+
+    let mut out = Vec::new();
+    if let (Some(lo), Some(ro)) = (lhs.as_object(), rhs.as_object()) {
+        let mut keys: std::collections::BTreeSet<&String> = lo.keys().collect();
+        keys.extend(ro.keys());
+        for key in keys {
+            if lo.get(key) != ro.get(key) {
+                out.push(key.clone());
+            }
+        }
+    }
+    out
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -1646,6 +1760,41 @@ mod tests {
         let _ = std::fs::remove_file(path);
     }
 
+    #[test]
+    fn classify_sni_change_requires_restart() {
+        // censorship.* is not in overlay_hot_fields -> restart.
+        let old = ProxyConfig::default();
+        let mut new = ProxyConfig::default();
+        new.censorship.tls_domain = "front.example".to_string();
+
+        let class = classify_config_changes(&old, &new);
+        assert!(class.restart_required);
+        assert!(class.changed.iter().any(|c| c == "censorship"));
+    }
+
+    #[test]
+    fn classify_dns_overrides_change_is_hot() {
+        // network.dns_overrides IS in overlay_hot_fields -> no restart.
+        let old = ProxyConfig::default();
+        let mut new = ProxyConfig::default();
+        new.network.dns_overrides.push("1.1.1.1".to_string());
+
+        let class = classify_config_changes(&old, &new);
+        assert!(!class.restart_required);
+        assert!(class.changed.iter().any(|c| c == "network"));
+    }
+
+    #[test]
+    fn classify_timeouts_change_requires_restart() {
+        // timeouts.* is NOT in overlay_hot_fields -> restart.
+        let old = ProxyConfig::default();
+        let mut new = ProxyConfig::default();
+        new.timeouts.client_handshake = old.timeouts.client_handshake + 1;
+
+        let class = classify_config_changes(&old, &new);
+        assert!(class.restart_required);
+    }
+
     #[test]
     fn reload_recovers_after_parse_error_on_next_attempt() {
         let initial_tag = "cccccccccccccccccccccccccccccccc";

src/config/load.rs

@@ -299,6 +299,7 @@ const SERVER_CONFIG_KEYS: &[&str] = &[
     "listen_unix_sock",
     "listen_unix_sock_perm",
     "listen_tcp",
+    "client_mss",
     "proxy_protocol",
     "proxy_protocol_header_timeout_ms",
     "proxy_protocol_trusted_cidrs",
@@ -344,6 +345,11 @@ const CONNTRACK_CONTROL_CONFIG_KEYS: &[&str] = &[
 const LISTENER_CONFIG_KEYS: &[&str] = &[
     "ip",
     "port",
+    "client_mss",
+    "synlimit",
+    "synlimit_seconds",
+    "synlimit_hitcount",
+    "synlimit_burst",
     "announce",
     "announce_ip",
     "proxy_protocol",
@@ -370,6 +376,7 @@ const CENSORSHIP_CONFIG_KEYS: &[&str] = &[
     "tls_fetch_scope",
     "tls_fetch",
     "mask",
+    "mask_dynamic",
     "mask_host",
     "mask_port",
     "exclusive_mask",
@@ -411,6 +418,7 @@ const TLS_FETCH_CONFIG_KEYS: &[&str] = &[
 
 const ACCESS_CONFIG_KEYS: &[&str] = &[
     "users",
+    "user_enabled",
     "user_ad_tags",
     "user_max_tcp_conns",
     "user_max_tcp_conns_global_each",
@@ -1006,6 +1014,14 @@ fn validate_upstreams(config: &ProxyConfig) -> Result<()> {
                 "upstream.ipv4 and upstream.ipv6 cannot both be false".to_string(),
             ));
         }
+        if let Some(prefer) = upstream.prefer
+            && prefer != 4
+            && prefer != 6
+        {
+            return Err(ProxyError::Config(
+                "upstream.prefer must be 4 or 6".to_string(),
+            ));
+        }
 
         if let UpstreamType::Shadowsocks { url, .. } = &upstream.upstream_type {
             let parsed = ShadowsocksServerConfig::from_url(url)
@@ -1021,6 +1037,26 @@ fn validate_upstreams(config: &ProxyConfig) -> Result<()> {
     Ok(())
 }
 
+fn normalize_upstream_family_policy(config: &mut ProxyConfig) {
+    for (idx, upstream) in config.upstreams.iter_mut().enumerate() {
+        if matches!(upstream.ipv4, Some(false)) && upstream.prefer == Some(4) {
+            warn!(
+                upstream = idx,
+                "upstream.prefer=4 but upstream.ipv4=false; forcing prefer=6"
+            );
+            upstream.prefer = Some(6);
+        }
+
+        if matches!(upstream.ipv6, Some(false)) && upstream.prefer == Some(6) {
+            warn!(
+                upstream = idx,
+                "upstream.prefer=6 but upstream.ipv6=false; forcing prefer=4"
+            );
+            upstream.prefer = Some(4);
+        }
+    }
+}
+
 // ============= Main Config =============
 
 #[derive(Debug, Clone, Serialize, Deserialize, Default)]
@@ -1904,6 +1940,42 @@ impl ProxyConfig {
             ));
         }
 
+        if config.server.listen_backlog == 0 || config.server.listen_backlog > i32::MAX as u32 {
+            return Err(ProxyError::Config(format!(
+                "server.listen_backlog must be within [1, {}]",
+                i32::MAX
+            )));
+        }
+
+        config
+            .server
+            .client_mss_value()
+            .map_err(|error| ProxyError::Config(format!("server.client_mss {error}")))?;
+        for (idx, listener) in config.server.listeners.iter().enumerate() {
+            if listener.client_mss.is_some() {
+                listener
+                    .effective_client_mss(&config.server)
+                    .map_err(|error| {
+                        ProxyError::Config(format!("server.listeners[{idx}].client_mss {error}"))
+                    })?;
+            }
+            if listener.synlimit_seconds == 0 {
+                return Err(ProxyError::Config(format!(
+                    "server.listeners[{idx}].synlimit_seconds must be > 0"
+                )));
+            }
+            if listener.synlimit_hitcount == 0 {
+                return Err(ProxyError::Config(format!(
+                    "server.listeners[{idx}].synlimit_hitcount must be > 0"
+                )));
+            }
+            if listener.synlimit_burst == 0 {
+                return Err(ProxyError::Config(format!(
+                    "server.listeners[{idx}].synlimit_burst must be > 0"
+                )));
+            }
+        }
+
         if config.server.accept_permit_timeout_ms > 60_000 {
             return Err(ProxyError::Config(
                 "server.accept_permit_timeout_ms must be within [0, 60000]".to_string(),
@@ -2002,11 +2074,6 @@ impl ProxyConfig {
             *mask_host = normalize_mask_host_to_ascii(mask_host, "censorship.mask_host")?;
         }
 
-        // Default mask_host to tls_domain if not set and no unix socket configured.
-        if config.censorship.mask_host.is_none() && config.censorship.mask_unix_sock.is_none() {
-            config.censorship.mask_host = Some(config.censorship.tls_domain.clone());
-        }
-
         for (domain, target) in &config.censorship.exclusive_mask {
             if !is_valid_tls_domain_name(domain) {
                 return Err(ProxyError::Config(format!(
@@ -2144,6 +2211,11 @@ impl ProxyConfig {
                 config.server.listeners.push(ListenerConfig {
                     ip: ipv4,
                     port: Some(config.server.port),
+                    client_mss: None,
+                    synlimit: SynLimitMode::default(),
+                    synlimit_seconds: default_synlimit_seconds(),
+                    synlimit_hitcount: default_synlimit_hitcount(),
+                    synlimit_burst: default_synlimit_burst(),
                     announce: None,
                     announce_ip: None,
                     proxy_protocol: None,
@@ -2156,6 +2228,11 @@ impl ProxyConfig {
                 config.server.listeners.push(ListenerConfig {
                     ip: ipv6,
                     port: Some(config.server.port),
+                    client_mss: None,
+                    synlimit: SynLimitMode::default(),
+                    synlimit_seconds: default_synlimit_seconds(),
+                    synlimit_hitcount: default_synlimit_hitcount(),
+                    synlimit_burst: default_synlimit_burst(),
                     announce: None,
                     announce_ip: None,
                     proxy_protocol: None,
@@ -2199,8 +2276,10 @@ impl ProxyConfig {
                 selected_scope: String::new(),
                 ipv4: None,
                 ipv6: None,
+                prefer: None,
             });
         }
+        normalize_upstream_family_policy(&mut config);
 
         // Ensure default DC203 override is present.
         config
@@ -2429,6 +2508,7 @@ mod tests {
         assert_eq!(cfg.general.update_every, default_update_every());
         assert_eq!(cfg.server.listen_addr_ipv4, default_listen_addr_ipv4());
         assert_eq!(cfg.server.listen_addr_ipv6, default_listen_addr_ipv6_opt());
+        assert_eq!(cfg.server.client_mss_value(), Ok(None));
         assert_eq!(
             cfg.server.proxy_protocol_trusted_cidrs,
             default_proxy_protocol_trusted_cidrs()
@@ -3756,6 +3836,153 @@ mod tests {
         let _ = std::fs::remove_file(path);
     }
 
+    #[test]
+    fn client_mss_presets_and_listener_override_are_resolved() {
+        let toml = r#"
+            [server]
+            client_mss = "tspu"
+
+            [[server.listeners]]
+            ip = "127.0.0.1"
+            port = 1443
+
+            [[server.listeners]]
+            ip = "127.0.0.2"
+            port = 1444
+            client_mss = "2in8"
+
+            [[server.listeners]]
+            ip = "127.0.0.3"
+            port = 1445
+            client_mss = ""
+
+            [[server.listeners]]
+            ip = "127.0.0.4"
+            port = 1446
+            client_mss = "extreme-low"
+
+            [censorship]
+            tls_domain = "example.com"
+
+            [access.users]
+            user = "00000000000000000000000000000000"
+        "#;
+        let dir = std::env::temp_dir();
+        let path = dir.join("telemt_client_mss_valid_test.toml");
+        std::fs::write(&path, toml).unwrap();
+        let cfg = ProxyConfig::load(&path).unwrap();
+
+        assert_eq!(cfg.server.client_mss_value(), Ok(Some(92)));
+        assert_eq!(
+            cfg.server.listeners[0].effective_client_mss(&cfg.server),
+            Ok(Some(92))
+        );
+        assert_eq!(
+            cfg.server.listeners[1].effective_client_mss(&cfg.server),
+            Ok(Some(256))
+        );
+        assert_eq!(
+            cfg.server.listeners[2].effective_client_mss(&cfg.server),
+            Ok(None)
+        );
+        assert_eq!(
+            cfg.server.listeners[3].effective_client_mss(&cfg.server),
+            Ok(Some(88))
+        );
+        let _ = std::fs::remove_file(path);
+    }
+
+    #[test]
+    fn client_mss_custom_value_is_accepted() {
+        let toml = r#"
+            [server]
+            client_mss = "4096"
+
+            [censorship]
+            tls_domain = "example.com"
+
+            [access.users]
+            user = "00000000000000000000000000000000"
+        "#;
+        let dir = std::env::temp_dir();
+        let path = dir.join("telemt_client_mss_custom_valid_test.toml");
+        std::fs::write(&path, toml).unwrap();
+        let cfg = ProxyConfig::load(&path).unwrap();
+
+        assert_eq!(cfg.server.client_mss_value(), Ok(Some(4096)));
+        let _ = std::fs::remove_file(path);
+    }
+
+    #[test]
+    fn client_mss_out_of_range_is_rejected() {
+        for value in ["87", "4097"] {
+            let toml = format!(
+                r#"
+                [server]
+                client_mss = "{value}"
+
+                [censorship]
+                tls_domain = "example.com"
+
+                [access.users]
+                user = "00000000000000000000000000000000"
+            "#
+            );
+            let dir = std::env::temp_dir();
+            let path = dir.join(format!("telemt_client_mss_out_of_range_{value}_test.toml"));
+            std::fs::write(&path, toml).unwrap();
+            let err = ProxyConfig::load(&path).unwrap_err().to_string();
+
+            assert!(err.contains("server.client_mss custom value must be within [88, 4096]"));
+            let _ = std::fs::remove_file(path);
+        }
+    }
+
+    #[test]
+    fn client_mss_unquoted_number_is_rejected() {
+        let toml = r#"
+            [server]
+            client_mss = 256
+
+            [censorship]
+            tls_domain = "example.com"
+
+            [access.users]
+            user = "00000000000000000000000000000000"
+        "#;
+        let dir = std::env::temp_dir();
+        let path = dir.join("telemt_client_mss_unquoted_number_test.toml");
+        std::fs::write(&path, toml).unwrap();
+        let err = ProxyConfig::load(&path).unwrap_err().to_string();
+
+        assert!(err.contains("client_mss"));
+        let _ = std::fs::remove_file(path);
+    }
+
+    #[test]
+    fn listener_client_mss_invalid_preset_is_rejected() {
+        let toml = r#"
+            [[server.listeners]]
+            ip = "127.0.0.1"
+            port = 1443
+            client_mss = "tiny"
+
+            [censorship]
+            tls_domain = "example.com"
+
+            [access.users]
+            user = "00000000000000000000000000000000"
+        "#;
+        let dir = std::env::temp_dir();
+        let path = dir.join("telemt_listener_client_mss_invalid_test.toml");
+        std::fs::write(&path, toml).unwrap();
+        let err = ProxyConfig::load(&path).unwrap_err().to_string();
+
+        assert!(err.contains("server.listeners[0].client_mss"));
+        assert!(err.contains("must be \"\", extreme-low, tspu, 2in8"));
+        let _ = std::fs::remove_file(path);
+    }
+
     #[test]
     fn api_runtime_edge_cache_ttl_out_of_range_is_rejected() {
         let toml = r#"

src/config/tests/load_mask_shape_security_tests.rs

@@ -1,14 +1,21 @@
 use super::*;
 use std::fs;
 use std::path::PathBuf;
+use std::sync::atomic::{AtomicU64, Ordering};
 use std::time::{SystemTime, UNIX_EPOCH};
 
+static TEMP_CONFIG_COUNTER: AtomicU64 = AtomicU64::new(0);
+
 fn write_temp_config(contents: &str) -> PathBuf {
     let nonce = SystemTime::now()
         .duration_since(UNIX_EPOCH)
         .expect("system time must be after unix epoch")
         .as_nanos();
-    let path = std::env::temp_dir().join(format!("telemt-load-mask-shape-security-{nonce}.toml"));
+    let seq = TEMP_CONFIG_COUNTER.fetch_add(1, Ordering::Relaxed);
+    let pid = std::process::id();
+    let path = std::env::temp_dir().join(format!(
+        "telemt-load-mask-shape-security-{pid}-{seq}-{nonce}.toml"
+    ));
     fs::write(&path, contents).expect("temp config write must succeed");
     path
 }

src/config/tests/load_memory_envelope_tests.rs

@@ -95,6 +95,44 @@ max_client_frame = 16777217
     remove_temp_config(&path);
 }
 
+#[test]
+fn load_rejects_listen_backlog_above_i32_upper_bound() {
+    let path = write_temp_config(
+        r#"
+[server]
+listen_backlog = 2147483648
+"#,
+    );
+
+    let err = ProxyConfig::load(&path).expect_err("listen_backlog above socket cap must fail");
+    let msg = err.to_string();
+    assert!(
+        msg.contains("server.listen_backlog must be within [1, 2147483647]"),
+        "error must explain listen_backlog hard cap, got: {msg}"
+    );
+
+    remove_temp_config(&path);
+}
+
+#[test]
+fn load_rejects_zero_listen_backlog() {
+    let path = write_temp_config(
+        r#"
+[server]
+listen_backlog = 0
+"#,
+    );
+
+    let err = ProxyConfig::load(&path).expect_err("zero listen_backlog must fail");
+    let msg = err.to_string();
+    assert!(
+        msg.contains("server.listen_backlog must be within [1, 2147483647]"),
+        "error must explain listen_backlog lower bound, got: {msg}"
+    );
+
+    remove_temp_config(&path);
+}
+
 #[test]
 fn load_accepts_memory_limits_at_hard_upper_bounds() {
     let path = write_temp_config(

src/config/types.rs

@@ -429,7 +429,7 @@ pub struct GeneralConfig {
     pub ad_tag: Option<String>,
 
     /// Public IP override for middle-proxy NAT environments.
-    /// When set, this IP is used in ME key derivation and RPC_PROXY_REQ "our_addr".
+    /// When set, this IP is used in ME key derivation and local address translation.
     #[serde(default)]
     pub middle_proxy_nat_ip: Option<IpAddr>,
 
@@ -1369,6 +1369,77 @@ impl ConntrackPressureProfile {
     }
 }
 
+/// Per-listener SYN limiter mode.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub enum SynLimitMode {
+    /// Disable SYN limiting for this listener.
+    #[default]
+    Off,
+    /// Use iptables/ip6tables filter rules with the hashlimit match.
+    Iptables,
+    /// Use nftables rules with per-source token-bucket meters.
+    Nftables,
+}
+
+impl Serialize for SynLimitMode {
+    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        match self {
+            Self::Off => serializer.serialize_bool(false),
+            Self::Iptables => serializer.serialize_str("iptables"),
+            Self::Nftables => serializer.serialize_str("nftables"),
+        }
+    }
+}
+
+impl<'de> Deserialize<'de> for SynLimitMode {
+    fn deserialize<D>(deserializer: D) -> std::result::Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        struct SynLimitModeVisitor;
+
+        impl<'de> serde::de::Visitor<'de> for SynLimitModeVisitor {
+            type Value = SynLimitMode;
+
+            fn expecting(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+                formatter.write_str("false, iptables, or nftables")
+            }
+
+            fn visit_bool<E>(self, value: bool) -> std::result::Result<Self::Value, E>
+            where
+                E: serde::de::Error,
+            {
+                if value {
+                    Err(E::custom(
+                        "synlimit=true is ambiguous; use \"iptables\" or \"nftables\"",
+                    ))
+                } else {
+                    Ok(SynLimitMode::Off)
+                }
+            }
+
+            fn visit_str<E>(self, value: &str) -> std::result::Result<Self::Value, E>
+            where
+                E: serde::de::Error,
+            {
+                match value.trim().to_ascii_lowercase().as_str() {
+                    "false" | "off" | "disabled" | "none" => Ok(SynLimitMode::Off),
+                    "iptables" => Ok(SynLimitMode::Iptables),
+                    "nftables" => Ok(SynLimitMode::Nftables),
+                    _ => Err(E::custom(
+                        "synlimit must be false, \"iptables\", or \"nftables\"",
+                    )),
+                }
+            }
+        }
+
+        deserializer.deserialize_any(SynLimitModeVisitor)
+    }
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ConntrackControlConfig {
     /// Enables runtime conntrack-control worker for pressure mitigation.
@@ -1451,6 +1522,11 @@ pub struct ServerConfig {
     #[serde(default)]
     pub listen_tcp: Option<bool>,
 
+    /// Client-facing TCP MSS preset or custom value for all TCP listeners.
+    /// Empty string or omitted value keeps the kernel default.
+    #[serde(default)]
+    pub client_mss: Option<String>,
+
     /// Accept HAProxy PROXY protocol headers on incoming connections.
     /// When enabled, real client IPs are extracted from PROXY v1/v2 headers.
     #[serde(default)]
@@ -1517,6 +1593,7 @@ impl Default for ServerConfig {
             listen_unix_sock: None,
             listen_unix_sock_perm: None,
             listen_tcp: None,
+            client_mss: None,
             proxy_protocol: false,
             proxy_protocol_header_timeout_ms: default_proxy_protocol_header_timeout_ms(),
             proxy_protocol_trusted_cidrs: default_proxy_protocol_trusted_cidrs(),
@@ -1720,6 +1797,10 @@ pub struct AntiCensorshipConfig {
     #[serde(default = "default_true")]
     pub mask: bool,
 
+    /// Use the ClientHello SNI as the mask TCP target for configured TLS domains.
+    #[serde(default = "default_true")]
+    pub mask_dynamic: bool,
+
     #[serde(default)]
     pub mask_host: Option<String>,
 
@@ -1855,6 +1936,7 @@ impl Default for AntiCensorshipConfig {
             tls_fetch_scope: default_tls_fetch_scope(),
             tls_fetch: TlsFetchConfig::default(),
             mask: default_true(),
+            mask_dynamic: default_true(),
             mask_host: None,
             mask_port: default_mask_port(),
             exclusive_mask: HashMap::new(),
@@ -1892,6 +1974,9 @@ pub struct AccessConfig {
     #[serde(default = "default_access_users")]
     pub users: HashMap<String, String>,
 
+    #[serde(default)]
+    pub user_enabled: HashMap<String, bool>,
+
     /// Per-user ad_tag (32 hex chars from @MTProxybot).
     #[serde(default)]
     pub user_ad_tags: HashMap<String, String>,
@@ -1963,6 +2048,7 @@ impl Default for AccessConfig {
     fn default() -> Self {
         Self {
             users: default_access_users(),
+            user_enabled: HashMap::new(),
             user_ad_tags: HashMap::new(),
             user_max_tcp_conns: HashMap::new(),
             user_max_tcp_conns_global_each: default_user_max_tcp_conns_global_each(),
@@ -1983,6 +2069,10 @@ impl Default for AccessConfig {
 }
 
 impl AccessConfig {
+    pub fn is_user_enabled(&self, username: &str) -> bool {
+        self.user_enabled.get(username).copied().unwrap_or(true)
+    }
+
     /// Returns true if `ip` is contained in any CIDR listed for `username` under `user_source_deny`.
     pub fn is_user_source_ip_denied(&self, username: &str, ip: IpAddr) -> bool {
         self.user_source_deny
@@ -2057,6 +2147,20 @@ pub struct UpstreamConfig {
     /// `None` means auto-detect from runtime connectivity state.
     #[serde(default)]
     pub ipv6: Option<bool>,
+    /// Per-upstream IP family preference for Telegram DC targets.
+    /// `None` inherits the effective global `[network].prefer` decision.
+    #[serde(default)]
+    pub prefer: Option<u8>,
+}
+
+impl UpstreamConfig {
+    pub fn prefer_ipv6(&self, default_prefer_ipv6: bool) -> bool {
+        match self.prefer {
+            Some(6) => true,
+            Some(4) => false,
+            _ => default_prefer_ipv6,
+        }
+    }
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -2065,6 +2169,22 @@ pub struct ListenerConfig {
     /// Per-listener TCP port. If omitted, falls back to legacy `server.port`.
     #[serde(default)]
     pub port: Option<u16>,
+    /// Per-listener client-facing TCP MSS preset or custom value.
+    /// Empty string disables MSS shaping for this listener.
+    #[serde(default)]
+    pub client_mss: Option<String>,
+    /// Per-listener SYN limiter mode.
+    #[serde(default)]
+    pub synlimit: SynLimitMode,
+    /// Token-bucket rate interval for the per-listener SYN limiter.
+    #[serde(default = "default_synlimit_seconds")]
+    pub synlimit_seconds: u32,
+    /// Token-bucket rate amount for the per-listener SYN limiter.
+    #[serde(default = "default_synlimit_hitcount")]
+    pub synlimit_hitcount: u32,
+    /// Token-bucket burst size for the per-listener SYN limiter.
+    #[serde(default = "default_synlimit_burst")]
+    pub synlimit_burst: u32,
     /// IP address or hostname to announce in proxy links.
     /// Takes precedence over `announce_ip` if both are set.
     #[serde(default)]
@@ -2082,6 +2202,64 @@ pub struct ListenerConfig {
     pub reuse_allow: bool,
 }
 
+/// Client-facing TCP MSS preset for extreme-low fragmentation profiles.
+pub const CLIENT_MSS_EXTREME_LOW: u16 = 88;
+/// Client-facing TCP MSS preset matching TSPU-oriented deployments.
+pub const CLIENT_MSS_TSPU: u16 = 92;
+/// Client-facing TCP MSS preset for 2-in-8 segment shaping.
+pub const CLIENT_MSS_2IN8: u16 = 256;
+/// Minimum accepted custom client-facing TCP MSS value.
+pub const CLIENT_MSS_MIN: u16 = CLIENT_MSS_EXTREME_LOW;
+/// Maximum accepted custom client-facing TCP MSS value.
+pub const CLIENT_MSS_MAX: u16 = 4096;
+
+impl ServerConfig {
+    /// Resolves the global client-facing TCP MSS setting.
+    pub fn client_mss_value(&self) -> std::result::Result<Option<u16>, String> {
+        parse_client_mss(self.client_mss.as_deref())
+    }
+}
+
+impl ListenerConfig {
+    /// Resolves the listener MSS override, falling back to the global server value.
+    pub fn effective_client_mss(
+        &self,
+        server: &ServerConfig,
+    ) -> std::result::Result<Option<u16>, String> {
+        match self.client_mss.as_deref() {
+            Some(value) => parse_client_mss(Some(value)),
+            None => server.client_mss_value(),
+        }
+    }
+}
+
+fn parse_client_mss(raw: Option<&str>) -> std::result::Result<Option<u16>, String> {
+    let Some(raw) = raw else {
+        return Ok(None);
+    };
+    let value = raw.trim();
+    if value.is_empty() {
+        return Ok(None);
+    }
+
+    match value.to_ascii_lowercase().as_str() {
+        "extreme-low" => return Ok(Some(CLIENT_MSS_EXTREME_LOW)),
+        "tspu" => return Ok(Some(CLIENT_MSS_TSPU)),
+        "2in8" => return Ok(Some(CLIENT_MSS_2IN8)),
+        _ => {}
+    }
+
+    let parsed = value
+        .parse::<u16>()
+        .map_err(|_| "must be \"\", extreme-low, tspu, 2in8, or a decimal value".to_string())?;
+    if !(CLIENT_MSS_MIN..=CLIENT_MSS_MAX).contains(&parsed) {
+        return Err(format!(
+            "custom value must be within [{CLIENT_MSS_MIN}, {CLIENT_MSS_MAX}]"
+        ));
+    }
+    Ok(Some(parsed))
+}
+
 // ============= ShowLink =============
 
 /// Controls which users' proxy links are displayed at startup.

src/conntrack_control.rs

@@ -705,7 +705,7 @@ fn nofile_soft_limit() -> Option<u64> {
         if rc != 0 {
             return None;
         }
-        return Some(lim.rlim_cur);
+        return Some(lim.rlim_cur.into());
     }
     #[cfg(not(target_os = "linux"))]
     {

src/error.rs

@@ -245,6 +245,9 @@ pub enum ProxyError {
     InvalidSecret { user: String, reason: String },
 
     // ============= User Errors =============
+    #[error("User {user} disabled")]
+    UserDisabled { user: String },
+
     #[error("User {user} expired")]
     UserExpired { user: String },
 

src/maestro/connectivity.rs

@@ -147,7 +147,7 @@ pub(crate) async fn run_startup_connectivity(
             .any(|r| r.rtt_ms.is_some());
 
         if upstream_result.both_available {
-            if prefer_ipv6 {
+            if upstream_result.prefer_ipv6 {
                 info!("  IPv6 in use / IPv4 is fallback");
             } else {
                 info!("  IPv4 in use / IPv6 is fallback");

src/maestro/helpers.rs

@@ -1,6 +1,7 @@
 #![allow(clippy::items_after_test_module)]
 
 use std::path::{Path, PathBuf};
+use std::sync::atomic::{AtomicBool, Ordering};
 use std::time::Duration;
 
 use tokio::sync::watch;
@@ -18,8 +19,27 @@ use crate::transport::middle_proxy::{
 const MAESTRO_COLOR: &str = "\x1b[92m";
 const COLOR_RESET: &str = "\x1b[0m";
 
+static MAESTRO_COLORS_ENABLED: AtomicBool = AtomicBool::new(true);
+
+/// Enables or disables ANSI color in direct MAESTRO status lines.
+pub(crate) fn set_maestro_colors_enabled(enabled: bool) {
+    MAESTRO_COLORS_ENABLED.store(enabled, Ordering::Relaxed);
+}
+
+fn format_maestro_line(message: impl AsRef<str>, colors_enabled: bool) -> String {
+    if colors_enabled {
+        format!("{MAESTRO_COLOR}MAESTRO{COLOR_RESET}: {}", message.as_ref())
+    } else {
+        format!("MAESTRO: {}", message.as_ref())
+    }
+}
+
+/// Prints a direct MAESTRO status line outside the tracing subscriber.
 pub(crate) fn print_maestro_line(message: impl AsRef<str>) {
-    eprintln!("{MAESTRO_COLOR}MAESTRO{COLOR_RESET}: {}", message.as_ref());
+    eprintln!(
+        "{}",
+        format_maestro_line(message, MAESTRO_COLORS_ENABLED.load(Ordering::Relaxed))
+    );
 }
 
 pub(crate) fn resolve_runtime_config_path(
@@ -274,11 +294,24 @@ mod tests {
     use std::path::{Path, PathBuf};
 
     use super::{
-        expected_handshake_close_description, is_expected_handshake_eof, peer_close_description,
-        resolve_runtime_base_dir, resolve_runtime_config_path,
+        expected_handshake_close_description, format_maestro_line, is_expected_handshake_eof,
+        peer_close_description, resolve_runtime_base_dir, resolve_runtime_config_path,
     };
     use crate::error::{ProxyError, StreamError};
 
+    #[test]
+    fn maestro_line_formatter_respects_disabled_colors() {
+        let plain = format_maestro_line("boot", false);
+        assert_eq!(plain, "MAESTRO: boot");
+        assert!(!plain.contains('\x1b'));
+    }
+
+    #[test]
+    fn maestro_line_formatter_keeps_color_when_enabled() {
+        let colored = format_maestro_line("boot", true);
+        assert!(colored.contains("\x1b[92mMAESTRO\x1b[0m"));
+    }
+
     #[test]
     fn resolve_runtime_config_path_anchors_relative_to_startup_cwd() {
         let nonce = std::time::SystemTime::now()

src/maestro/listeners.rs

@@ -47,6 +47,10 @@ fn default_link_port(config: &ProxyConfig) -> u16 {
         .unwrap_or(config.server.port)
 }
 
+fn mss_segment_multiplier(client_mss: u16) -> u16 {
+    1460u16.div_ceil(client_mss)
+}
+
 #[allow(clippy::too_many_arguments)]
 pub(crate) async fn bind_listeners(
     config: &Arc<ProxyConfig>,
@@ -90,10 +94,22 @@ pub(crate) async fn bind_listeners(
             warn!(%addr, "Skipping IPv6 listener: IPv6 disabled by [network]");
             continue;
         }
+        let client_mss = match listener_conf.effective_client_mss(&config.server) {
+            Ok(value) => value,
+            Err(error) => {
+                warn!(
+                    %addr,
+                    error = %error,
+                    "Invalid listener client MSS after config validation; using kernel default"
+                );
+                None
+            }
+        };
         let options = ListenOptions {
             reuse_port: listener_conf.reuse_allow,
             ipv6_only: listener_conf.ip.is_ipv6(),
             backlog: config.server.listen_backlog,
+            client_mss,
             ..Default::default()
         };
 
@@ -101,6 +117,14 @@ pub(crate) async fn bind_listeners(
             Ok(socket) => {
                 let listener = TcpListener::from_std(socket.into())?;
                 info!("Listening on {}", addr);
+                if let Some(client_mss) = client_mss {
+                    info!(
+                        %addr,
+                        client_mss,
+                        segment_multiplier = mss_segment_multiplier(client_mss),
+                        "Client-facing TCP MSS configured"
+                    );
+                }
                 let listener_proxy_protocol = listener_conf
                     .proxy_protocol
                     .unwrap_or(config.server.proxy_protocol);

src/maestro/me_startup.rs

@@ -208,6 +208,8 @@ pub(crate) async fn initialize_me_pool(
                     me_nat_probe,
                     None,
                     config.network.stun_servers.clone(),
+                    config.network.stun_tcp_fallback,
+                    config.network.http_ip_detect_urls.clone(),
                     config.general.stun_nat_probe_concurrency,
                     probe.detected_ipv6,
                     config.timeouts.me_one_retry,

src/maestro/mod.rs

@@ -45,10 +45,12 @@ use crate::stats::beobachten::BeobachtenStore;
 use crate::stats::telemetry::TelemetryPolicy;
 use crate::stats::{ReplayChecker, Stats};
 use crate::stream::BufferPool;
+use crate::synlimit_control;
 use crate::transport::UpstreamManager;
 use crate::transport::middle_proxy::MePool;
 use helpers::{
     parse_cli, print_maestro_line, resolve_runtime_base_dir, resolve_runtime_config_path,
+    set_maestro_colors_enabled,
 };
 
 #[cfg(unix)]
@@ -314,6 +316,7 @@ async fn run_telemt_core(
         eprintln!("[telemt] Invalid network.dns_overrides: {}", e);
         std::process::exit(1);
     }
+    set_maestro_colors_enabled(!config.general.disable_colors);
     startup_tracker
         .complete_component(COMPONENT_CONFIG_LOAD, Some("config is ready".to_string()))
         .await;
@@ -462,6 +465,12 @@ async fn run_telemt_core(
             config.network.dns_overrides.len()
         );
     }
+    let shared_state = ProxySharedState::new();
+    shared_state.apply_user_enabled_config(&config.access.user_enabled);
+    shared_state.traffic_limiter.apply_policy(
+        config.access.user_rate_limits.clone(),
+        config.access.cidr_rate_limits.clone(),
+    );
 
     let (api_config_tx, api_config_rx) = watch::channel(Arc::new(config.clone()));
     let (detected_ips_tx, detected_ips_rx) = watch::channel((None::<IpAddr>, None::<IpAddr>));
@@ -500,6 +509,7 @@ async fn run_telemt_core(
             let me_pool_api = api_me_pool.clone();
             let upstream_manager_api = upstream_manager.clone();
             let route_runtime_api = route_runtime.clone();
+            let proxy_shared_api = shared_state.clone();
             let config_rx_api = api_config_rx.clone();
             let admission_rx_api = admission_rx.clone();
             let config_path_api = config_path.clone();
@@ -513,6 +523,7 @@ async fn run_telemt_core(
                     ip_tracker_api,
                     me_pool_api,
                     route_runtime_api,
+                    proxy_shared_api,
                     upstream_manager_api,
                     config_rx_api,
                     admission_rx_api,
@@ -730,11 +741,6 @@ async fn run_telemt_core(
     ));
 
     let buffer_pool = Arc::new(BufferPool::with_config(64 * 1024, 4096));
-    let shared_state = ProxySharedState::new();
-    shared_state.traffic_limiter.apply_policy(
-        config.access.user_rate_limits.clone(),
-        config.access.cidr_rate_limits.clone(),
-    );
 
     if direct_first_startup {
         startup_tracker
@@ -904,6 +910,9 @@ async fn run_telemt_core(
     // On Unix, caller supplies privilege drop after bind (may require root for port < 1024).
     drop_after_bind();
 
+    synlimit_control::reconcile_synlimit_rules(&config).await;
+    synlimit_control::spawn_synlimit_controller(config_rx.clone());
+
     runtime_tasks::apply_runtime_log_filter(
         has_rust_log,
         &effective_log_level,

src/maestro/runtime_tasks.rs

@@ -3,7 +3,7 @@ use std::path::Path;
 use std::sync::Arc;
 
 use tokio::sync::{mpsc, watch};
-use tracing::{debug, warn};
+use tracing::{debug, info, warn};
 use tracing_subscriber::EnvFilter;
 use tracing_subscriber::reload;
 
@@ -234,6 +234,27 @@ pub(crate) async fn spawn_runtime_tasks(
         }
     });
 
+    let shared_user_enabled = shared_state.clone();
+    let mut config_rx_user_enabled = config_rx.clone();
+    tokio::spawn(async move {
+        loop {
+            if config_rx_user_enabled.changed().await.is_err() {
+                break;
+            }
+            let cfg = config_rx_user_enabled.borrow_and_update().clone();
+            for user in shared_user_enabled.apply_user_enabled_config(&cfg.access.user_enabled) {
+                let cancelled = shared_user_enabled.cancel_user_sessions(&user);
+                if cancelled > 0 {
+                    info!(
+                        user = %user,
+                        cancelled,
+                        "Disabled user sessions cancelled after config reload"
+                    );
+                }
+            }
+        }
+    });
+
     let beobachten_writer = beobachten.clone();
     let config_rx_beobachten = config_rx.clone();
     tokio::spawn(async move {

src/maestro/shutdown.rs

@@ -19,6 +19,7 @@ use tokio::signal::unix::{SignalKind, signal};
 use tracing::{info, warn};
 
 use crate::stats::Stats;
+use crate::synlimit_control;
 use crate::transport::middle_proxy::MePool;
 
 use super::helpers::{format_uptime, unit_label};
@@ -102,6 +103,10 @@ async fn perform_shutdown(
     let uptime_secs = process_started_at.elapsed().as_secs();
     info!("Uptime: {}", format_uptime(uptime_secs));
 
+    if let Err(error) = synlimit_control::clear_synlimit_rules_all_backends().await {
+        warn!(error = %error, "Failed to clear SYN limiter rules during shutdown");
+    }
+
     // Graceful ME pool shutdown
     if let Some(pool) = &me_pool {
         match tokio::time::timeout(Duration::from_secs(2), pool.shutdown_send_close_conn_all())

src/main.rs

@@ -30,6 +30,7 @@ mod service;
 mod startup;
 mod stats;
 mod stream;
+mod synlimit_control;
 mod tls_front;
 mod transport;
 mod util;

src/metrics.rs

@@ -55,8 +55,10 @@ pub async fn serve(
                 return;
             }
         };
-        let is_ipv6 = addr.is_ipv6();
-        match bind_metrics_listener(addr, is_ipv6, listen_backlog) {
+        // Match `server.api.listen`: `[::]:port` is a dual-stack wildcard
+        // on Linux when `net.ipv6.bindv6only=0`.
+        let ipv6_only = addr.is_ipv6() && !addr.ip().is_unspecified();
+        match bind_metrics_listener(addr, ipv6_only, listen_backlog) {
             Ok(listener) => {
                 info!("Metrics endpoint: http://{}/metrics and /beobachten", addr);
                 serve_listener(
@@ -286,7 +288,7 @@ async fn handle<B>(
     }
 
     if req.uri().path() == "/beobachten" {
-        let body = render_beobachten(beobachten, config);
+        let body = render_beobachten(stats, beobachten, config);
         let resp = Response::builder()
             .status(StatusCode::OK)
             .header("content-type", "text/plain; charset=utf-8")
@@ -302,13 +304,22 @@ async fn handle<B>(
     Ok(resp)
 }
 
-fn render_beobachten(beobachten: &BeobachtenStore, config: &ProxyConfig) -> String {
+fn render_beobachten(stats: &Stats, beobachten: &BeobachtenStore, config: &ProxyConfig) -> String {
     if !config.general.beobachten {
         return "beobachten disabled\n".to_string();
     }
 
     let ttl = Duration::from_secs(config.general.beobachten_minutes.saturating_mul(60));
-    beobachten.snapshot_text(ttl)
+    let mut body = beobachten.snapshot_text(ttl);
+    let tls_text = stats.tls_fingerprint_snapshot_text(ttl, 20);
+    if !tls_text.is_empty() {
+        if !body.ends_with('\n') {
+            body.push('\n');
+        }
+        body.push('\n');
+        body.push_str(&tls_text);
+    }
+    body
 }
 
 fn tls_front_domains(config: &ProxyConfig) -> Vec<String> {
@@ -370,11 +381,32 @@ async fn render_tls_front_profile_health(
         "# HELP telemt_tls_front_profile_info TLS front profile source and feature flags per configured domain"
     );
     let _ = writeln!(out, "# TYPE telemt_tls_front_profile_info gauge");
+    let _ = writeln!(
+        out,
+        "# HELP telemt_tls_front_profile_quality_info TLS front profile quality and key-share group per configured domain"
+    );
+    let _ = writeln!(out, "# TYPE telemt_tls_front_profile_quality_info gauge");
     let _ = writeln!(
         out,
         "# HELP telemt_tls_front_profile_age_seconds Age of cached TLS front profile data per configured domain"
     );
     let _ = writeln!(out, "# TYPE telemt_tls_front_profile_age_seconds gauge");
+    let _ = writeln!(
+        out,
+        "# HELP telemt_tls_front_profile_server_hello_bytes TLS front cached ServerHello record body bytes per configured domain"
+    );
+    let _ = writeln!(
+        out,
+        "# TYPE telemt_tls_front_profile_server_hello_bytes gauge"
+    );
+    let _ = writeln!(
+        out,
+        "# HELP telemt_tls_front_profile_server_hello_extensions TLS front cached visible ServerHello extension count per configured domain"
+    );
+    let _ = writeln!(
+        out,
+        "# TYPE telemt_tls_front_profile_server_hello_extensions gauge"
+    );
     let _ = writeln!(
         out,
         "# HELP telemt_tls_front_profile_app_data_records TLS front cached app-data record count per configured domain"
@@ -409,11 +441,26 @@ async fn render_tls_front_profile_health(
             "telemt_tls_front_profile_info{{domain=\"{}\",source=\"{}\",is_default=\"{}\",has_cert_info=\"{}\",has_cert_payload=\"{}\"}} 1",
             domain, item.source, item.is_default, item.has_cert_info, item.has_cert_payload
         );
+        let _ = writeln!(
+            out,
+            "telemt_tls_front_profile_quality_info{{domain=\"{}\",quality=\"{}\",key_share_group=\"{}\"}} 1",
+            domain, item.quality, item.key_share_group
+        );
         let _ = writeln!(
             out,
             "telemt_tls_front_profile_age_seconds{{domain=\"{}\"}} {}",
             domain, item.age_seconds
         );
+        let _ = writeln!(
+            out,
+            "telemt_tls_front_profile_server_hello_bytes{{domain=\"{}\"}} {}",
+            domain, item.server_hello_record_len
+        );
+        let _ = writeln!(
+            out,
+            "telemt_tls_front_profile_server_hello_extensions{{domain=\"{}\"}} {}",
+            domain, item.server_hello_extensions
+        );
         let _ = writeln!(
             out,
             "telemt_tls_front_profile_app_data_records{{domain=\"{}\"}} {}",
@@ -3890,7 +3937,20 @@ mod tests {
                         session_id: Vec::new(),
                         cipher_suite: [0x13, 0x01],
                         compression: 0,
-                        extensions: Vec::new(),
+                        extensions: {
+                            let mut key_share = vec![0x00, 0x1d, 0x00, 0x20];
+                            key_share.resize(36, 0x42);
+                            vec![
+                                crate::tls_front::types::TlsExtension {
+                                    ext_type: 0x002b,
+                                    data: vec![0x03, 0x04],
+                                },
+                                crate::tls_front::types::TlsExtension {
+                                    ext_type: 0x0033,
+                                    data: key_share,
+                                },
+                            ]
+                        },
                     },
                     cert_info: None,
                     cert_payload: Some(TlsCertPayload {
@@ -3904,6 +3964,7 @@ mod tests {
                         app_data_record_sizes: vec![1024, 512],
                         ticket_record_sizes: vec![69],
                         source: TlsProfileSource::Merged,
+                        ..TlsBehaviorProfile::default()
                     },
                     fetched_at: SystemTime::now(),
                     domain: "primary.example".to_string(),
@@ -3922,6 +3983,18 @@ mod tests {
         assert!(
             output.contains("telemt_tls_front_profile_info{domain=\"fallback.example\",source=\"default\",is_default=\"true\",has_cert_info=\"false\",has_cert_payload=\"false\"} 1")
         );
+        assert!(
+            output.contains("telemt_tls_front_profile_quality_info{domain=\"primary.example\",quality=\"raw_strict\",key_share_group=\"x25519\"} 1")
+        );
+        assert!(
+            output.contains("telemt_tls_front_profile_quality_info{domain=\"fallback.example\",quality=\"fallback\",key_share_group=\"none\"} 1")
+        );
+        assert!(output.contains(
+            "telemt_tls_front_profile_server_hello_bytes{domain=\"primary.example\"} 90"
+        ));
+        assert!(output.contains(
+            "telemt_tls_front_profile_server_hello_extensions{domain=\"primary.example\"} 2"
+        ));
         assert!(
             output.contains(
                 "telemt_tls_front_profile_app_data_records{domain=\"primary.example\"} 2"
@@ -4034,7 +4107,10 @@ mod tests {
         );
         assert!(output.contains("# TYPE telemt_tls_front_profile_domains gauge"));
         assert!(output.contains("# TYPE telemt_tls_front_profile_info gauge"));
+        assert!(output.contains("# TYPE telemt_tls_front_profile_quality_info gauge"));
         assert!(output.contains("# TYPE telemt_tls_front_profile_age_seconds gauge"));
+        assert!(output.contains("# TYPE telemt_tls_front_profile_server_hello_bytes gauge"));
+        assert!(output.contains("# TYPE telemt_tls_front_profile_server_hello_extensions gauge"));
         assert!(output.contains("# TYPE telemt_tls_front_profile_app_data_records gauge"));
         assert!(output.contains("# TYPE telemt_tls_front_profile_ticket_records gauge"));
         assert!(

src/network/probe.rs

@@ -12,7 +12,7 @@ use tracing::{debug, info, warn};
 use crate::config::{NetworkConfig, UpstreamConfig, UpstreamType};
 use crate::error::Result;
 use crate::network::stun::{
-    DualStunResult, IpFamily, StunProbeResult, stun_probe_family_with_bind,
+    DualStunResult, IpFamily, StunProbeResult, stun_probe_family_with_bind_and_tcp_fallback,
 };
 use crate::transport::UpstreamManager;
 
@@ -58,6 +58,7 @@ impl NetworkDecision {
 }
 
 const STUN_BATCH_TIMEOUT: Duration = Duration::from_secs(5);
+const STUN_BATCH_TCP_FALLBACK_TIMEOUT: Duration = Duration::from_secs(12);
 
 pub async fn run_probe(
     config: &NetworkConfig,
@@ -81,8 +82,14 @@ pub async fn run_probe(
             warn!("STUN probe is enabled but network.stun_servers is empty");
             DualStunResult::default()
         } else {
-            probe_stun_servers_parallel(&servers, stun_nat_probe_concurrency.max(1), None, None)
-                .await
+            probe_stun_servers_parallel(
+                &servers,
+                stun_nat_probe_concurrency.max(1),
+                None,
+                None,
+                config.stun_tcp_fallback,
+            )
+            .await
         }
     } else if nat_probe {
         info!("STUN probe is disabled by network.stun_use=false");
@@ -163,6 +170,7 @@ pub async fn run_probe(
             stun_nat_probe_concurrency.max(1),
             bind_v4,
             bind_v6,
+            config.stun_tcp_fallback,
         )
         .await;
         if let Some(reflected) = direct_stun_res.v4.map(|r| r.reflected_addr) {
@@ -234,7 +242,7 @@ pub async fn run_probe(
     Ok(probe)
 }
 
-async fn detect_public_ipv4_http(urls: &[String]) -> Option<Ipv4Addr> {
+pub(crate) async fn detect_public_ipv4_http(urls: &[String]) -> Option<Ipv4Addr> {
     let client = reqwest::Client::builder()
         .timeout(Duration::from_secs(3))
         .build()
@@ -277,6 +285,7 @@ async fn probe_stun_servers_parallel(
     concurrency: usize,
     bind_v4: Option<IpAddr>,
     bind_v6: Option<IpAddr>,
+    tcp_fallback: bool,
 ) -> DualStunResult {
     let mut join_set = JoinSet::new();
     let mut next_idx = 0usize;
@@ -288,9 +297,26 @@ async fn probe_stun_servers_parallel(
             let stun_addr = servers[next_idx].clone();
             next_idx += 1;
             join_set.spawn(async move {
-                let res = timeout(STUN_BATCH_TIMEOUT, async {
-                    let v4 = stun_probe_family_with_bind(&stun_addr, IpFamily::V4, bind_v4).await?;
-                    let v6 = stun_probe_family_with_bind(&stun_addr, IpFamily::V6, bind_v6).await?;
+                let batch_timeout = if tcp_fallback {
+                    STUN_BATCH_TCP_FALLBACK_TIMEOUT
+                } else {
+                    STUN_BATCH_TIMEOUT
+                };
+                let res = timeout(batch_timeout, async {
+                    let v4 = stun_probe_family_with_bind_and_tcp_fallback(
+                        &stun_addr,
+                        IpFamily::V4,
+                        bind_v4,
+                        tcp_fallback,
+                    )
+                    .await?;
+                    let v6 = stun_probe_family_with_bind_and_tcp_fallback(
+                        &stun_addr,
+                        IpFamily::V6,
+                        bind_v6,
+                        tcp_fallback,
+                    )
+                    .await?;
                     Ok::<DualStunResult, crate::error::ProxyError>(DualStunResult { v4, v6 })
                 })
                 .await;

src/network/stun.rs

@@ -4,7 +4,8 @@
 use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr};
 use std::sync::OnceLock;
 
-use tokio::net::{UdpSocket, lookup_host};
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+use tokio::net::{TcpSocket, UdpSocket, lookup_host};
 use tokio::time::{Duration, sleep, timeout};
 
 use crate::crypto::SecureRandom;
@@ -36,9 +37,16 @@ pub struct DualStunResult {
 }
 
 pub async fn stun_probe_dual(stun_addr: &str) -> Result<DualStunResult> {
+    stun_probe_dual_with_tcp_fallback(stun_addr, false).await
+}
+
+pub async fn stun_probe_dual_with_tcp_fallback(
+    stun_addr: &str,
+    tcp_fallback: bool,
+) -> Result<DualStunResult> {
     let (v4, v6) = tokio::join!(
-        stun_probe_family(stun_addr, IpFamily::V4),
-        stun_probe_family(stun_addr, IpFamily::V6),
+        stun_probe_family_with_tcp_fallback(stun_addr, IpFamily::V4, tcp_fallback),
+        stun_probe_family_with_tcp_fallback(stun_addr, IpFamily::V6, tcp_fallback),
     );
 
     Ok(DualStunResult { v4: v4?, v6: v6? })
@@ -48,13 +56,44 @@ pub async fn stun_probe_family(
     stun_addr: &str,
     family: IpFamily,
 ) -> Result<Option<StunProbeResult>> {
-    stun_probe_family_with_bind(stun_addr, family, None).await
+    stun_probe_family_with_tcp_fallback(stun_addr, family, false).await
+}
+
+pub async fn stun_probe_family_with_tcp_fallback(
+    stun_addr: &str,
+    family: IpFamily,
+    tcp_fallback: bool,
+) -> Result<Option<StunProbeResult>> {
+    stun_probe_family_with_bind_and_tcp_fallback(stun_addr, family, None, tcp_fallback).await
 }
 
 pub async fn stun_probe_family_with_bind(
     stun_addr: &str,
     family: IpFamily,
     bind_ip: Option<IpAddr>,
+) -> Result<Option<StunProbeResult>> {
+    stun_probe_family_with_bind_and_tcp_fallback(stun_addr, family, bind_ip, false).await
+}
+
+pub async fn stun_probe_family_with_bind_and_tcp_fallback(
+    stun_addr: &str,
+    family: IpFamily,
+    bind_ip: Option<IpAddr>,
+    tcp_fallback: bool,
+) -> Result<Option<StunProbeResult>> {
+    let udp_attempts = if tcp_fallback { 1 } else { 3 };
+    let udp_result = stun_probe_family_udp(stun_addr, family, bind_ip, udp_attempts).await?;
+    if udp_result.is_some() || !tcp_fallback {
+        return Ok(udp_result);
+    }
+    stun_probe_family_tcp(stun_addr, family, bind_ip).await
+}
+
+async fn stun_probe_family_udp(
+    stun_addr: &str,
+    family: IpFamily,
+    bind_ip: Option<IpAddr>,
+    max_attempts: u8,
 ) -> Result<Option<StunProbeResult>> {
     let bind_addr = match (family, bind_ip) {
         (IpFamily::V4, Some(IpAddr::V4(ip))) => SocketAddr::new(IpAddr::V4(ip), 0),
@@ -94,12 +133,7 @@ pub async fn stun_probe_family_with_bind(
         return Ok(None);
     }
 
-    let mut req = [0u8; 20];
-    req[0..2].copy_from_slice(&0x0001u16.to_be_bytes()); // Binding Request
-    req[2..4].copy_from_slice(&0u16.to_be_bytes()); // length
-    req[4..8].copy_from_slice(&0x2112A442u32.to_be_bytes()); // magic cookie
-    stun_rng().fill(&mut req[8..20]); // transaction ID
-
+    let req = build_binding_request();
     let mut buf = [0u8; 256];
     let mut attempt = 0;
     let mut backoff = Duration::from_secs(1);
@@ -115,7 +149,7 @@ pub async fn stun_probe_family_with_bind(
             Ok(Err(e)) => return Err(ProxyError::Proxy(format!("STUN recv failed: {e}"))),
             Err(_) => {
                 attempt += 1;
-                if attempt >= 3 {
+                if attempt >= max_attempts {
                     return Ok(None);
                 }
                 sleep(backoff).await;
@@ -128,19 +162,139 @@ pub async fn stun_probe_family_with_bind(
             return Ok(None);
         }
 
-        let magic = 0x2112A442u32.to_be_bytes();
         let txid = &req[8..20];
-        let mut idx = 20;
-        while idx + 4 <= n {
-            let atype = u16::from_be_bytes(buf[idx..idx + 2].try_into().unwrap());
-            let alen = u16::from_be_bytes(buf[idx + 2..idx + 4].try_into().unwrap()) as usize;
-            idx += 4;
-            if idx + alen > n {
-                break;
-            }
+        if let Some(reflected_addr) = parse_reflected_addr(&buf[..n], txid) {
+            let local_addr = socket
+                .local_addr()
+                .map_err(|e| ProxyError::Proxy(format!("STUN local_addr failed: {e}")))?;
+            return Ok(Some(StunProbeResult {
+                local_addr,
+                reflected_addr,
+                family,
+            }));
+        }
+    }
 
-            match atype {
-            0x0020 /* XOR-MAPPED-ADDRESS */ | 0x0001 /* MAPPED-ADDRESS */ => {
+    Ok(None)
+}
+
+async fn stun_probe_family_tcp(
+    stun_addr: &str,
+    family: IpFamily,
+    bind_ip: Option<IpAddr>,
+) -> Result<Option<StunProbeResult>> {
+    let target_addr = match resolve_stun_addr(stun_addr, family).await? {
+        Some(addr) => addr,
+        None => return Ok(None),
+    };
+    let socket = match family {
+        IpFamily::V4 => TcpSocket::new_v4(),
+        IpFamily::V6 => TcpSocket::new_v6(),
+    }
+    .map_err(|e| ProxyError::Proxy(format!("STUN TCP socket failed: {e}")))?;
+    match (family, bind_ip) {
+        (IpFamily::V4, Some(IpAddr::V4(ip))) => {
+            if socket.bind(SocketAddr::new(IpAddr::V4(ip), 0)).is_err() {
+                return Ok(None);
+            }
+        }
+        (IpFamily::V6, Some(IpAddr::V6(ip))) => {
+            if socket.bind(SocketAddr::new(IpAddr::V6(ip), 0)).is_err() {
+                return Ok(None);
+            }
+        }
+        (IpFamily::V4, Some(IpAddr::V6(_))) | (IpFamily::V6, Some(IpAddr::V4(_))) => {
+            return Ok(None);
+        }
+        (_, None) => {}
+    }
+
+    let connect_res = timeout(Duration::from_secs(3), socket.connect(target_addr)).await;
+    let mut stream = match connect_res {
+        Ok(Ok(stream)) => stream,
+        Ok(Err(e))
+            if family == IpFamily::V6
+                && matches!(
+                    e.kind(),
+                    std::io::ErrorKind::NetworkUnreachable
+                        | std::io::ErrorKind::HostUnreachable
+                        | std::io::ErrorKind::Unsupported
+                        | std::io::ErrorKind::NetworkDown
+                ) =>
+        {
+            return Ok(None);
+        }
+        Ok(Err(e)) => return Err(ProxyError::Proxy(format!("STUN TCP connect failed: {e}"))),
+        Err(_) => return Ok(None),
+    };
+
+    let req = build_binding_request();
+    timeout(Duration::from_secs(3), stream.write_all(&req))
+        .await
+        .map_err(|_| ProxyError::Proxy("STUN TCP send timeout".to_string()))?
+        .map_err(|e| ProxyError::Proxy(format!("STUN TCP send failed: {e}")))?;
+
+    let mut header = [0u8; 20];
+    timeout(Duration::from_secs(3), stream.read_exact(&mut header))
+        .await
+        .map_err(|_| ProxyError::Proxy("STUN TCP header timeout".to_string()))?
+        .map_err(|e| ProxyError::Proxy(format!("STUN TCP header read failed: {e}")))?;
+    let body_len = u16::from_be_bytes([header[2], header[3]]) as usize;
+    if body_len > 236 {
+        return Ok(None);
+    }
+    let mut buf = [0u8; 256];
+    buf[..20].copy_from_slice(&header);
+    if body_len > 0 {
+        timeout(
+            Duration::from_secs(3),
+            stream.read_exact(&mut buf[20..20 + body_len]),
+        )
+        .await
+        .map_err(|_| ProxyError::Proxy("STUN TCP body timeout".to_string()))?
+        .map_err(|e| ProxyError::Proxy(format!("STUN TCP body read failed: {e}")))?;
+    }
+
+    let txid = &req[8..20];
+    let Some(reflected_addr) = parse_reflected_addr(&buf[..20 + body_len], txid) else {
+        return Ok(None);
+    };
+    let local_addr = stream
+        .local_addr()
+        .map_err(|e| ProxyError::Proxy(format!("STUN TCP local_addr failed: {e}")))?;
+    Ok(Some(StunProbeResult {
+        local_addr,
+        reflected_addr,
+        family,
+    }))
+}
+
+fn build_binding_request() -> [u8; 20] {
+    let mut req = [0u8; 20];
+    req[0..2].copy_from_slice(&0x0001u16.to_be_bytes());
+    req[2..4].copy_from_slice(&0u16.to_be_bytes());
+    req[4..8].copy_from_slice(&0x2112A442u32.to_be_bytes());
+    stun_rng().fill(&mut req[8..20]);
+    req
+}
+
+fn parse_reflected_addr(buf: &[u8], txid: &[u8]) -> Option<SocketAddr> {
+    if buf.len() < 20 {
+        return None;
+    }
+
+    let magic = 0x2112A442u32.to_be_bytes();
+    let mut idx = 20;
+    while idx + 4 <= buf.len() {
+        let atype = u16::from_be_bytes(buf[idx..idx + 2].try_into().ok()?);
+        let alen = u16::from_be_bytes(buf[idx + 2..idx + 4].try_into().ok()?) as usize;
+        idx += 4;
+        if idx + alen > buf.len() {
+            break;
+        }
+
+        match atype {
+            0x0020 | 0x0001 => {
                 if alen < 8 {
                     break;
                 }
@@ -157,7 +311,6 @@ pub async fn stun_probe_family_with_bind(
 
                 let raw_ip = &buf[idx + 4..idx + 4 + len_check];
                 let mut port = u16::from_be_bytes(port_bytes);
-
                 let reflected_ip = if atype == 0x0020 {
                     port ^= ((magic[0] as u16) << 8) | magic[1] as u16;
                     match family_byte {
@@ -172,7 +325,9 @@ pub async fn stun_probe_family_with_bind(
                         }
                         0x02 => {
                             let mut ip = [0u8; 16];
-                            let xor_key = [magic.as_slice(), txid].concat();
+                            let mut xor_key = [0u8; 16];
+                            xor_key[..4].copy_from_slice(&magic);
+                            xor_key[4..].copy_from_slice(txid.get(..12)?);
                             for (i, b) in raw_ip.iter().enumerate().take(16) {
                                 ip[i] = *b ^ xor_key[i];
                             }
@@ -185,34 +340,24 @@ pub async fn stun_probe_family_with_bind(
                     }
                 } else {
                     match family_byte {
-                        0x01 => IpAddr::V4(Ipv4Addr::new(raw_ip[0], raw_ip[1], raw_ip[2], raw_ip[3])),
-                        0x02 => IpAddr::V6(Ipv6Addr::from(<[u8; 16]>::try_from(raw_ip).unwrap())),
+                        0x01 => {
+                            IpAddr::V4(Ipv4Addr::new(raw_ip[0], raw_ip[1], raw_ip[2], raw_ip[3]))
+                        }
+                        0x02 => IpAddr::V6(Ipv6Addr::from(<[u8; 16]>::try_from(raw_ip).ok()?)),
                         _ => {
                             idx += (alen + 3) & !3;
                             continue;
                         }
                     }
                 };
-
-                let reflected_addr = SocketAddr::new(reflected_ip, port);
-                let local_addr = socket
-                    .local_addr()
-                    .map_err(|e| ProxyError::Proxy(format!("STUN local_addr failed: {e}")))?;
-
-                return Ok(Some(StunProbeResult {
-                    local_addr,
-                    reflected_addr,
-                    family,
-                }));
+                return Some(SocketAddr::new(reflected_ip, port));
             }
             _ => {}
         }
 
-            idx += (alen + 3) & !3;
-        }
+        idx += (alen + 3) & !3;
     }
-
-    Ok(None)
+    None
 }
 
 async fn resolve_stun_addr(stun_addr: &str, family: IpFamily) -> Result<Option<SocketAddr>> {
@@ -245,3 +390,58 @@ async fn resolve_stun_addr(stun_addr: &str, family: IpFamily) -> Result<Option<S
     });
     Ok(target)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn parse_reflected_addr_reads_mapped_ipv4() {
+        let txid = [0u8; 12];
+        let mut response = [0u8; 32];
+        response[0..2].copy_from_slice(&0x0101u16.to_be_bytes());
+        response[2..4].copy_from_slice(&12u16.to_be_bytes());
+        response[4..8].copy_from_slice(&0x2112A442u32.to_be_bytes());
+        response[20..22].copy_from_slice(&0x0001u16.to_be_bytes());
+        response[22..24].copy_from_slice(&8u16.to_be_bytes());
+        response[25] = 0x01;
+        response[26..28].copy_from_slice(&443u16.to_be_bytes());
+        response[28..32].copy_from_slice(&[203, 0, 113, 9]);
+
+        let reflected = parse_reflected_addr(&response, &txid).unwrap();
+        assert_eq!(
+            reflected,
+            SocketAddr::new(IpAddr::V4(Ipv4Addr::new(203, 0, 113, 9)), 443)
+        );
+    }
+
+    #[test]
+    fn parse_reflected_addr_reads_xor_mapped_ipv4() {
+        let txid = [0u8; 12];
+        let magic = 0x2112A442u32.to_be_bytes();
+        let port = 443u16;
+        let ip = [203u8, 0, 113, 9];
+        let xport = port ^ (((magic[0] as u16) << 8) | magic[1] as u16);
+        let xip = [
+            ip[0] ^ magic[0],
+            ip[1] ^ magic[1],
+            ip[2] ^ magic[2],
+            ip[3] ^ magic[3],
+        ];
+        let mut response = [0u8; 32];
+        response[0..2].copy_from_slice(&0x0101u16.to_be_bytes());
+        response[2..4].copy_from_slice(&12u16.to_be_bytes());
+        response[4..8].copy_from_slice(&0x2112A442u32.to_be_bytes());
+        response[20..22].copy_from_slice(&0x0020u16.to_be_bytes());
+        response[22..24].copy_from_slice(&8u16.to_be_bytes());
+        response[25] = 0x01;
+        response[26..28].copy_from_slice(&xport.to_be_bytes());
+        response[28..32].copy_from_slice(&xip);
+
+        let reflected = parse_reflected_addr(&response, &txid).unwrap();
+        assert_eq!(
+            reflected,
+            SocketAddr::new(IpAddr::V4(Ipv4Addr::new(203, 0, 113, 9)), 443)
+        );
+    }
+}

src/protocol/constants.rs

@@ -5,6 +5,9 @@
 use std::net::{IpAddr, Ipv4Addr};
 
 use crate::crypto::SecureRandom;
+use crate::protocol::framing::{
+    secure_version_d_body_len_from_wire_len, secure_version_d_padding_len,
+};
 use std::sync::LazyLock;
 
 // ============= Telegram Datacenters =============
@@ -236,22 +239,20 @@ pub fn is_valid_secure_payload_len(data_len: usize) -> bool {
 }
 
 /// Compute Secure Intermediate payload length from wire length.
-/// Secure mode strips up to 3 random tail bytes by truncating to 4-byte boundary.
+/// Secure mode cannot distinguish full-word padding from payload, so only the
+/// non-aligned tail bytes are stripped.
 pub fn secure_payload_len_from_wire_len(wire_len: usize) -> Option<usize> {
-    if wire_len < 4 {
-        return None;
-    }
-    Some(wire_len - (wire_len % 4))
+    secure_version_d_body_len_from_wire_len(wire_len)
 }
 
 /// Generate padding length for Secure Intermediate protocol.
-/// Data must be 4-byte aligned; padding is 1..=3 so total is never divisible by 4.
+/// Telegram Desktop uses a 4-bit random padding length for VersionD packets.
 pub fn secure_padding_len(data_len: usize, rng: &SecureRandom) -> usize {
     debug_assert!(
         is_valid_secure_payload_len(data_len),
         "Secure payload must be 4-byte aligned, got {data_len}"
     );
-    rng.range(3) + 1
+    secure_version_d_padding_len(rng)
 }
 
 // ============= Timeouts =============
@@ -424,21 +425,15 @@ mod tests {
     }
 
     #[test]
-    fn secure_padding_never_produces_aligned_total() {
+    fn secure_padding_matches_tdesktop_range() {
         let rng = SecureRandom::new();
         for data_len in (0..1000).step_by(4) {
             for _ in 0..100 {
                 let padding = secure_padding_len(data_len, &rng);
                 assert!(
-                    padding <= 3,
+                    padding <= 15,
                     "padding out of range: data_len={data_len}, padding={padding}"
                 );
-                assert_ne!(
-                    (data_len + padding) % 4,
-                    0,
-                    "invariant violated: data_len={data_len}, padding={padding}, total={}",
-                    data_len + padding
-                );
             }
         }
     }
@@ -454,6 +449,16 @@ mod tests {
         }
     }
 
+    #[test]
+    fn secure_wire_len_preserves_full_word_tail() {
+        let payload_len = 64;
+        for padding in [4usize, 8, 12] {
+            let wire_len = payload_len + padding;
+            let recovered = secure_payload_len_from_wire_len(wire_len);
+            assert_eq!(recovered, Some(wire_len));
+        }
+    }
+
     #[test]
     fn secure_wire_len_rejects_too_short_frames() {
         assert_eq!(secure_payload_len_from_wire_len(0), None);

src/protocol/framing.rs

@@ -0,0 +1,92 @@
+//! Shared MTProto transport framing helpers.
+
+use crate::crypto::SecureRandom;
+
+/// QuickACK marker bit used by Intermediate and Secure Intermediate headers.
+pub(crate) const INTERMEDIATE_QUICKACK_FLAG: u32 = 0x8000_0000;
+
+/// Payload length mask used by Intermediate and Secure Intermediate headers.
+pub(crate) const INTERMEDIATE_WIRE_LEN_MASK: u32 = 0x7fff_ffff;
+
+/// Maximum random tail length used by Telegram Desktop VersionD packets.
+pub(crate) const SECURE_VERSION_D_PADDING_MAX: usize = 15;
+
+/// Parsed Intermediate/Secure Intermediate length header.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub(crate) struct IntermediateHeader {
+    /// Payload length on the wire, excluding the four-byte header.
+    pub(crate) wire_len: usize,
+    /// Whether the QuickACK marker bit was set in the length header.
+    pub(crate) quickack: bool,
+}
+
+/// Parse an Intermediate/Secure Intermediate length header.
+pub(crate) fn parse_intermediate_header(header: [u8; 4]) -> IntermediateHeader {
+    let raw = u32::from_le_bytes(header);
+    IntermediateHeader {
+        wire_len: (raw & INTERMEDIATE_WIRE_LEN_MASK) as usize,
+        quickack: (raw & INTERMEDIATE_QUICKACK_FLAG) != 0,
+    }
+}
+
+/// Encode an Intermediate/Secure Intermediate length header.
+pub(crate) fn encode_intermediate_header(wire_len: usize, quickack: bool) -> Option<u32> {
+    if wire_len > INTERMEDIATE_WIRE_LEN_MASK as usize {
+        return None;
+    }
+
+    let mut raw = u32::try_from(wire_len).ok()?;
+    if quickack {
+        raw |= INTERMEDIATE_QUICKACK_FLAG;
+    }
+    Some(raw)
+}
+
+/// Recover the VersionD body length visible to MTProto from the encrypted wire length.
+pub(crate) fn secure_version_d_body_len_from_wire_len(wire_len: usize) -> Option<usize> {
+    if wire_len < 4 {
+        return None;
+    }
+
+    Some(wire_len - (wire_len % 4))
+}
+
+/// Generate Telegram Desktop-compatible VersionD random tail length.
+pub(crate) fn secure_version_d_padding_len(rng: &SecureRandom) -> usize {
+    rng.range(SECURE_VERSION_D_PADDING_MAX + 1)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn intermediate_header_roundtrip_preserves_quickack_zero_length() {
+        let encoded = encode_intermediate_header(0, true).unwrap();
+        assert_eq!(encoded, INTERMEDIATE_QUICKACK_FLAG);
+
+        let parsed = parse_intermediate_header(encoded.to_le_bytes());
+        assert_eq!(parsed.wire_len, 0);
+        assert!(parsed.quickack);
+    }
+
+    #[test]
+    fn intermediate_header_rejects_lengths_above_31_bits() {
+        assert_eq!(
+            encode_intermediate_header(INTERMEDIATE_WIRE_LEN_MASK as usize, false),
+            Some(INTERMEDIATE_WIRE_LEN_MASK)
+        );
+        assert_eq!(
+            encode_intermediate_header(INTERMEDIATE_WIRE_LEN_MASK as usize + 1, false),
+            None
+        );
+    }
+
+    #[test]
+    fn secure_version_d_body_len_strips_only_non_word_tail() {
+        assert_eq!(secure_version_d_body_len_from_wire_len(3), None);
+        assert_eq!(secure_version_d_body_len_from_wire_len(8), Some(8));
+        assert_eq!(secure_version_d_body_len_from_wire_len(11), Some(8));
+        assert_eq!(secure_version_d_body_len_from_wire_len(12), Some(12));
+    }
+}

src/protocol/mod.rs

@@ -2,8 +2,10 @@
 
 pub mod constants;
 pub mod frame;
+pub(crate) mod framing;
 pub mod obfuscation;
 pub mod tls;
+pub mod tls_fingerprint;
 
 #[allow(unused_imports)]
 pub use constants::*;
@@ -13,3 +15,5 @@ pub use frame::*;
 pub use obfuscation::*;
 #[allow(unused_imports)]
 pub use tls::*;
+#[allow(unused_imports)]
+pub use tls_fingerprint::*;

src/protocol/tests/tls_security_tests.rs

@@ -1239,6 +1239,18 @@ fn test_gen_fake_x25519_key() {
     assert_ne!(key1, key2);
 }
 
+#[test]
+fn test_gen_fake_x25519mlkem768_server_key_share_shape() {
+    let rng = crate::crypto::SecureRandom::new();
+    let key_share = gen_fake_x25519mlkem768_server_key_share(&rng);
+
+    assert_eq!(key_share.len(), X25519MLKEM768_SERVER_KEY_SHARE_LEN);
+    assert!(
+        key_share.iter().any(|byte| *byte != 0),
+        "hybrid ServerHello key_share must not collapse to all-zero bytes"
+    );
+}
+
 #[test]
 fn test_fake_x25519_key_is_nonzero_and_varies() {
     let rng = crate::crypto::SecureRandom::new();
@@ -1325,6 +1337,69 @@ fn server_hello_extension_types(record: &[u8]) -> Vec<u16> {
     out
 }
 
+fn server_hello_key_share(record: &[u8]) -> Option<(u16, usize)> {
+    if record.len() < 9 || record[0] != TLS_RECORD_HANDSHAKE || record[5] != 0x02 {
+        return None;
+    }
+
+    let record_len = u16::from_be_bytes([record[3], record[4]]) as usize;
+    if record.len() < 5 + record_len {
+        return None;
+    }
+
+    let hs_len = u32::from_be_bytes([0, record[6], record[7], record[8]]) as usize;
+    let hs_start = 5;
+    let hs_end = hs_start + 4 + hs_len;
+    if hs_end > record.len() {
+        return None;
+    }
+
+    let mut pos = hs_start + 4 + 2 + 32;
+    if pos >= hs_end {
+        return None;
+    }
+    let sid_len = record[pos] as usize;
+    pos += 1 + sid_len;
+    if pos + 2 + 1 + 2 > hs_end {
+        return None;
+    }
+
+    pos += 2 + 1;
+    let ext_len = u16::from_be_bytes([record[pos], record[pos + 1]]) as usize;
+    pos += 2;
+    let ext_end = pos + ext_len;
+    if ext_end > hs_end {
+        return None;
+    }
+
+    while pos + 4 <= ext_end {
+        let etype = u16::from_be_bytes([record[pos], record[pos + 1]]);
+        let elen = u16::from_be_bytes([record[pos + 2], record[pos + 3]]) as usize;
+        pos += 4;
+        if pos + elen > ext_end {
+            return None;
+        }
+        if etype == extension_type::KEY_SHARE {
+            if elen < 4 {
+                return None;
+            }
+            let group = u16::from_be_bytes([record[pos], record[pos + 1]]);
+            let key_exchange_len = u16::from_be_bytes([record[pos + 2], record[pos + 3]]) as usize;
+            if 4 + key_exchange_len != elen {
+                return None;
+            }
+            return Some((group, key_exchange_len));
+        }
+        pos += elen;
+    }
+
+    None
+}
+
+fn test_server_key_share(group: u16, len: usize) -> ServerHelloKeyShare {
+    ServerHelloKeyShare::new(group, vec![0x42; len])
+}
+
 #[test]
 fn build_server_hello_never_places_alpn_in_server_hello_extensions() {
     let secret = b"alpn_sh_forbidden";
@@ -1372,6 +1447,7 @@ fn emulated_server_hello_never_places_alpn_in_server_hello_extensions() {
             app_data_record_sizes: vec![1024],
             ticket_record_sizes: Vec::new(),
             source: TlsProfileSource::Default,
+            ..TlsBehaviorProfile::default()
         },
         fetched_at: SystemTime::now(),
         domain: "example.com".to_string(),
@@ -1385,6 +1461,11 @@ fn emulated_server_hello_never_places_alpn_in_server_hello_extensions() {
         false,
         true,
         ClientHelloTlsVersion::Tls13,
+        [0x13, 0x01],
+        &test_server_key_share(
+            TLS_NAMED_GROUP_X25519MLKEM768,
+            X25519MLKEM768_SERVER_KEY_SHARE_LEN,
+        ),
         &rng,
         Some(b"h2".to_vec()),
         0,
@@ -1394,14 +1475,21 @@ fn emulated_server_hello_never_places_alpn_in_server_hello_extensions() {
         !exts.contains(&0x0010),
         "ALPN extension must not appear in emulated ServerHello"
     );
+    assert_eq!(
+        server_hello_key_share(&response),
+        Some((
+            TLS_NAMED_GROUP_X25519MLKEM768,
+            X25519MLKEM768_SERVER_KEY_SHARE_LEN
+        ))
+    );
 }
 
 #[test]
 fn test_tls_extension_builder() {
-    let key = [0x42u8; 32];
+    let key = vec![0x42u8; X25519MLKEM768_SERVER_KEY_SHARE_LEN];
 
     let mut builder = TlsExtensionBuilder::new();
-    builder.add_key_share(&key);
+    builder.add_key_share(TLS_NAMED_GROUP_X25519MLKEM768, &key);
     builder.add_supported_versions(0x0304);
 
     let result = builder.build();
@@ -1414,10 +1502,10 @@ fn test_tls_extension_builder() {
 #[test]
 fn test_server_hello_builder() {
     let session_id = vec![0x01, 0x02, 0x03, 0x04];
-    let key = [0x55u8; 32];
+    let key = vec![0x55u8; X25519MLKEM768_SERVER_KEY_SHARE_LEN];
 
     let builder = ServerHelloBuilder::new(session_id.clone())
-        .with_x25519_key(&key)
+        .with_key_share(TLS_NAMED_GROUP_X25519MLKEM768, &key)
         .with_tls13_version();
 
     let record = builder.build_record();
@@ -1451,6 +1539,41 @@ fn test_build_server_hello_structure() {
     let app_start = ccs_start + ccs_len;
     assert!(response.len() > app_start + 5);
     assert_eq!(response[app_start], TLS_RECORD_APPLICATION);
+
+    assert_eq!(
+        server_hello_key_share(&response),
+        Some((
+            TLS_NAMED_GROUP_X25519MLKEM768,
+            X25519MLKEM768_SERVER_KEY_SHARE_LEN
+        ))
+    );
+}
+
+#[test]
+fn test_build_server_hello_with_cipher_uses_selected_key_share_group() {
+    let secret = b"test secret";
+    let client_digest = [0x42u8; 32];
+    let session_id = vec![0xAA; 32];
+    let key_share =
+        ServerHelloKeyShare::new(TLS_NAMED_GROUP_X25519, vec![0x55u8; X25519_KEY_SHARE_LEN]);
+
+    let rng = crate::crypto::SecureRandom::new();
+    let response = build_server_hello_with_cipher(
+        secret,
+        &client_digest,
+        &session_id,
+        2048,
+        &rng,
+        [0x13, 0x01],
+        &key_share,
+        None,
+        0,
+    );
+
+    assert_eq!(
+        server_hello_key_share(&response),
+        Some((TLS_NAMED_GROUP_X25519, X25519_KEY_SHARE_LEN))
+    );
 }
 
 #[test]
@@ -1473,10 +1596,10 @@ fn test_build_server_hello_digest() {
 #[test]
 fn test_server_hello_extensions_length() {
     let session_id = vec![0x01; 32];
-    let key = [0x55u8; 32];
+    let key = vec![0x55u8; X25519MLKEM768_SERVER_KEY_SHARE_LEN];
 
     let builder = ServerHelloBuilder::new(session_id)
-        .with_x25519_key(&key)
+        .with_key_share(TLS_NAMED_GROUP_X25519MLKEM768, &key)
         .with_tls13_version();
 
     let record = builder.build_record();
@@ -1509,12 +1632,55 @@ fn test_validate_tls_handshake_format() {
 }
 
 fn build_client_hello_with_exts(exts: Vec<(u16, Vec<u8>)>, host: &str) -> Vec<u8> {
+    build_client_hello_with_ciphers_and_exts(&[[0x13, 0x01]], exts, host)
+}
+
+fn client_key_share_extension(entries: &[(u16, usize)]) -> Vec<u8> {
+    let mut shares = Vec::new();
+    for (group, key_exchange_len) in entries {
+        assert!(*key_exchange_len <= u16::MAX as usize);
+        shares.extend_from_slice(&group.to_be_bytes());
+        shares.extend_from_slice(&(*key_exchange_len as u16).to_be_bytes());
+        let start = shares.len();
+        shares.resize(start + *key_exchange_len, 0x42);
+    }
+
+    assert!(shares.len() <= u16::MAX as usize);
+    let mut extension = Vec::new();
+    extension.extend_from_slice(&(shares.len() as u16).to_be_bytes());
+    extension.extend_from_slice(&shares);
+    extension
+}
+
+fn client_key_share_extension_with_payloads(entries: &[(u16, &[u8])]) -> Vec<u8> {
+    let mut shares = Vec::new();
+    for (group, key_exchange) in entries {
+        assert!(key_exchange.len() <= u16::MAX as usize);
+        shares.extend_from_slice(&group.to_be_bytes());
+        shares.extend_from_slice(&(key_exchange.len() as u16).to_be_bytes());
+        shares.extend_from_slice(key_exchange);
+    }
+
+    assert!(shares.len() <= u16::MAX as usize);
+    let mut extension = Vec::new();
+    extension.extend_from_slice(&(shares.len() as u16).to_be_bytes());
+    extension.extend_from_slice(&shares);
+    extension
+}
+
+fn build_client_hello_with_ciphers_and_exts(
+    cipher_suites: &[[u8; 2]],
+    exts: Vec<(u16, Vec<u8>)>,
+    host: &str,
+) -> Vec<u8> {
     let mut body = Vec::new();
     body.extend_from_slice(&TLS_VERSION);
     body.extend_from_slice(&[0u8; 32]);
     body.push(0);
-    body.extend_from_slice(&2u16.to_be_bytes());
-    body.extend_from_slice(&[0x13, 0x01]);
+    body.extend_from_slice(&((cipher_suites.len() * 2) as u16).to_be_bytes());
+    for suite in cipher_suites {
+        body.extend_from_slice(suite);
+    }
     body.push(1);
     body.push(0);
 
@@ -1654,6 +1820,244 @@ fn detect_client_hello_tls_version_rejects_malformed_supported_versions() {
     assert!(detect_client_hello_tls_version(&ch).is_none());
 }
 
+#[test]
+fn select_server_hello_cipher_suite_keeps_profile_cipher_when_offered() {
+    let ch = build_client_hello_with_ciphers_and_exts(
+        &[[0x13, 0x01], [0x13, 0x03]],
+        Vec::new(),
+        "example.com",
+    );
+    assert_eq!(
+        select_server_hello_cipher_suite(&ch, [0x13, 0x03]),
+        Some([0x13, 0x03])
+    );
+}
+
+#[test]
+fn select_server_hello_cipher_suite_ignores_profile_tls12_cipher() {
+    let ch = build_client_hello_with_ciphers_and_exts(
+        &[[0xc0, 0x2f], [0x13, 0x03]],
+        Vec::new(),
+        "example.com",
+    );
+    assert_eq!(
+        select_server_hello_cipher_suite(&ch, [0xc0, 0x2f]),
+        Some([0x13, 0x03])
+    );
+}
+
+#[test]
+fn select_server_hello_cipher_suite_rejects_without_offered_tls13_suite() {
+    let ch = build_client_hello_with_ciphers_and_exts(&[[0xc0, 0x2f]], Vec::new(), "example.com");
+    assert_eq!(select_server_hello_cipher_suite(&ch, [0x13, 0x01]), None);
+}
+
+#[test]
+fn select_server_hello_cipher_suite_falls_back_to_offered_tls13_suite() {
+    let ch = build_client_hello_with_ciphers_and_exts(&[[0x13, 0x03]], Vec::new(), "example.com");
+    assert_eq!(
+        select_server_hello_cipher_suite(&ch, [0x13, 0x01]),
+        Some([0x13, 0x03])
+    );
+}
+
+#[test]
+fn select_server_hello_cipher_suite_rejects_malformed_clienthello() {
+    let mut ch =
+        build_client_hello_with_ciphers_and_exts(&[[0x13, 0x03]], Vec::new(), "example.com");
+    ch.truncate(12);
+    assert_eq!(select_server_hello_cipher_suite(&ch, [0x13, 0x01]), None);
+}
+
+#[test]
+fn select_server_hello_key_share_group_prefers_hybrid_when_valid_share_is_offered() {
+    let key_share = client_key_share_extension(&[
+        (0x0a0a, 1),
+        (
+            TLS_NAMED_GROUP_X25519MLKEM768,
+            X25519MLKEM768_CLIENT_KEY_SHARE_LEN,
+        ),
+        (TLS_NAMED_GROUP_X25519, X25519_KEY_SHARE_LEN),
+    ]);
+    let ch = build_client_hello_with_exts(vec![(0x0033, key_share)], "example.com");
+
+    assert_eq!(
+        select_server_hello_key_share_group(&ch),
+        Some(TLS_NAMED_GROUP_X25519MLKEM768)
+    );
+}
+
+#[test]
+fn select_server_hello_key_share_group_prefers_profiled_x25519_when_valid_share_is_offered() {
+    let key_share = client_key_share_extension(&[
+        (
+            TLS_NAMED_GROUP_X25519MLKEM768,
+            X25519MLKEM768_CLIENT_KEY_SHARE_LEN,
+        ),
+        (TLS_NAMED_GROUP_X25519, X25519_KEY_SHARE_LEN),
+    ]);
+    let ch = build_client_hello_with_exts(vec![(0x0033, key_share)], "example.com");
+
+    assert_eq!(
+        select_server_hello_key_share_group_with_preference(&ch, Some(TLS_NAMED_GROUP_X25519)),
+        Some(TLS_NAMED_GROUP_X25519)
+    );
+}
+
+#[test]
+fn build_x25519mlkem768_server_key_share_accepts_tdesktop_canonical_share() {
+    let key_share = client_key_share_extension(&[
+        (
+            TLS_NAMED_GROUP_X25519MLKEM768,
+            X25519MLKEM768_CLIENT_KEY_SHARE_LEN,
+        ),
+        (TLS_NAMED_GROUP_X25519, X25519_KEY_SHARE_LEN),
+    ]);
+    let ch = build_client_hello_with_exts(vec![(0x0033, key_share)], "example.com");
+    let rng = crate::crypto::SecureRandom::new();
+
+    let server_key_share = build_x25519mlkem768_server_key_share(&ch, &rng)
+        .expect("tdesktop-like canonical share must build a ServerHello share");
+
+    assert_eq!(server_key_share.len(), X25519MLKEM768_SERVER_KEY_SHARE_LEN);
+    assert!(
+        server_key_share[..MLKEM768_SERVER_CIPHERTEXT_LEN]
+            .iter()
+            .any(|byte| *byte != 0),
+        "ML-KEM ciphertext must not be all zero"
+    );
+    assert!(
+        server_key_share[MLKEM768_SERVER_CIPHERTEXT_LEN..]
+            .iter()
+            .any(|byte| *byte != 0),
+        "X25519 server share must not be all zero"
+    );
+}
+
+#[test]
+fn build_x25519_server_key_share_accepts_tdesktop_fallback_share() {
+    let key_share = client_key_share_extension(&[
+        (
+            TLS_NAMED_GROUP_X25519MLKEM768,
+            X25519MLKEM768_CLIENT_KEY_SHARE_LEN,
+        ),
+        (TLS_NAMED_GROUP_X25519, X25519_KEY_SHARE_LEN),
+    ]);
+    let ch = build_client_hello_with_exts(vec![(0x0033, key_share)], "example.com");
+    let rng = crate::crypto::SecureRandom::new();
+
+    let server_key_share = build_x25519_server_key_share(&ch, &rng)
+        .expect("tdesktop-like X25519 share must build a ServerHello share");
+
+    assert_eq!(server_key_share.len(), X25519_KEY_SHARE_LEN);
+    assert!(
+        server_key_share.iter().any(|byte| *byte != 0),
+        "X25519 server share must not be all zero"
+    );
+}
+
+#[test]
+fn build_server_hello_key_share_prefers_profiled_x25519() {
+    let key_share = client_key_share_extension(&[
+        (
+            TLS_NAMED_GROUP_X25519MLKEM768,
+            X25519MLKEM768_CLIENT_KEY_SHARE_LEN,
+        ),
+        (TLS_NAMED_GROUP_X25519, X25519_KEY_SHARE_LEN),
+    ]);
+    let ch = build_client_hello_with_exts(vec![(0x0033, key_share)], "example.com");
+    let rng = crate::crypto::SecureRandom::new();
+
+    let server_key_share = build_server_hello_key_share(&ch, Some(TLS_NAMED_GROUP_X25519), &rng)
+        .expect("profiled X25519 share must be selected when client offers it");
+
+    assert_eq!(server_key_share.group(), TLS_NAMED_GROUP_X25519);
+    assert_eq!(server_key_share.key_exchange().len(), X25519_KEY_SHARE_LEN);
+}
+
+#[test]
+fn build_server_hello_key_share_falls_back_from_bad_profiled_x25519_to_hybrid() {
+    let key_share = client_key_share_extension(&[(
+        TLS_NAMED_GROUP_X25519MLKEM768,
+        X25519MLKEM768_CLIENT_KEY_SHARE_LEN,
+    )]);
+    let ch = build_client_hello_with_exts(vec![(0x0033, key_share)], "example.com");
+    let rng = crate::crypto::SecureRandom::new();
+
+    let server_key_share = build_server_hello_key_share(&ch, Some(TLS_NAMED_GROUP_X25519), &rng)
+        .expect("hybrid share must be selected when profiled X25519 is unavailable");
+
+    assert_eq!(server_key_share.group(), TLS_NAMED_GROUP_X25519MLKEM768);
+    assert_eq!(
+        server_key_share.key_exchange().len(),
+        X25519MLKEM768_SERVER_KEY_SHARE_LEN
+    );
+}
+
+#[test]
+fn build_x25519mlkem768_server_key_share_rejects_noncanonical_mlkem_key() {
+    let mut key_exchange = vec![0x42; X25519MLKEM768_CLIENT_KEY_SHARE_LEN];
+    key_exchange[..3].copy_from_slice(&[0xff, 0xff, 0xff]);
+    let key_share = client_key_share_extension_with_payloads(&[(
+        TLS_NAMED_GROUP_X25519MLKEM768,
+        &key_exchange,
+    )]);
+    let ch = build_client_hello_with_exts(vec![(0x0033, key_share)], "example.com");
+    let rng = crate::crypto::SecureRandom::new();
+
+    assert!(build_x25519mlkem768_server_key_share(&ch, &rng).is_none());
+}
+
+#[test]
+fn build_x25519mlkem768_server_key_share_rejects_all_zero_x25519_share() {
+    let mut key_exchange = vec![0x42; X25519MLKEM768_CLIENT_KEY_SHARE_LEN];
+    key_exchange[MLKEM768_CLIENT_ENCAPSULATION_KEY_LEN..].fill(0);
+    let key_share = client_key_share_extension_with_payloads(&[(
+        TLS_NAMED_GROUP_X25519MLKEM768,
+        &key_exchange,
+    )]);
+    let ch = build_client_hello_with_exts(vec![(0x0033, key_share)], "example.com");
+    let rng = crate::crypto::SecureRandom::new();
+
+    assert!(build_x25519mlkem768_server_key_share(&ch, &rng).is_none());
+}
+
+#[test]
+fn select_server_hello_key_share_group_accepts_x25519_when_hybrid_is_absent() {
+    let key_share = client_key_share_extension(&[(TLS_NAMED_GROUP_X25519, X25519_KEY_SHARE_LEN)]);
+    let ch = build_client_hello_with_exts(vec![(0x0033, key_share)], "example.com");
+
+    assert_eq!(
+        select_server_hello_key_share_group(&ch),
+        Some(TLS_NAMED_GROUP_X25519)
+    );
+}
+
+#[test]
+fn select_server_hello_key_share_group_rejects_malformed_hybrid_len() {
+    let key_share = client_key_share_extension(&[(
+        TLS_NAMED_GROUP_X25519MLKEM768,
+        X25519MLKEM768_CLIENT_KEY_SHARE_LEN - 1,
+    )]);
+    let ch = build_client_hello_with_exts(vec![(0x0033, key_share)], "example.com");
+
+    assert_eq!(select_server_hello_key_share_group(&ch), None);
+}
+
+#[test]
+fn select_server_hello_key_share_group_rejects_malformed_key_share_tail() {
+    let mut key_share = client_key_share_extension(&[(
+        TLS_NAMED_GROUP_X25519MLKEM768,
+        X25519MLKEM768_CLIENT_KEY_SHARE_LEN,
+    )]);
+    let shares_len = u16::from_be_bytes([key_share[0], key_share[1]]) + 1;
+    key_share[0..2].copy_from_slice(&shares_len.to_be_bytes());
+    key_share.push(0);
+    let ch = build_client_hello_with_exts(vec![(0x0033, key_share)], "example.com");
+
+    assert_eq!(select_server_hello_key_share_group(&ch), None);
+}
+
 #[test]
 fn extract_sni_rejects_zero_length_host_name() {
     let mut sni_ext = Vec::new();
@@ -2179,7 +2583,7 @@ fn light_fuzz_boot_time_timestamp_matrix_with_short_replay_window_obeys_boot_cap
 }
 
 #[test]
-fn server_hello_application_data_contains_alpn_marker_when_selected() {
+fn server_hello_application_data_omits_alpn_marker_when_selected() {
     let secret = b"alpn_marker_test";
     let client_digest = [0x55u8; TLS_DIGEST_LEN];
     let session_id = vec![0xAB; 32];
@@ -2206,8 +2610,8 @@ fn server_hello_application_data_contains_alpn_marker_when_selected() {
     assert!(
         app_payload
             .windows(expected.len())
-            .any(|window| window == expected),
-        "first application payload must carry ALPN marker for selected protocol"
+            .all(|window| window != expected),
+        "first application payload must not expose plaintext ALPN marker bytes"
     );
 }
 
@@ -2303,14 +2707,14 @@ fn server_hello_ignores_oversized_alpn_when_marker_would_not_fit() {
 }
 
 #[test]
-fn server_hello_embeds_full_alpn_marker_when_it_exactly_fits_fake_cert_len() {
+fn server_hello_omits_alpn_marker_even_when_it_would_fit_fake_cert_len() {
     let secret = b"alpn_exact_fit_test";
     let client_digest = [0x58u8; TLS_DIGEST_LEN];
     let session_id = vec![0xA5; 32];
     let rng = crate::crypto::SecureRandom::new();
     let proto = vec![b'z'; 57];
 
-    // marker_len = 4 + (2 + (1 + proto_len)) = 7 + proto_len = 64
+    // marker_len = 4 + (2 + (1 + proto_len)) = 7 + proto_len = 64.
     let response = build_server_hello(
         secret,
         &client_digest,
@@ -2336,7 +2740,7 @@ fn server_hello_embeds_full_alpn_marker_when_it_exactly_fits_fake_cert_len() {
     expected_marker.extend_from_slice(&proto);
 
     assert_eq!(app_payload.len(), expected_marker.len());
-    assert_eq!(app_payload, expected_marker.as_slice());
+    assert_ne!(app_payload, expected_marker.as_slice());
 }
 
 #[test]

src/protocol/tls.rs

@@ -65,6 +65,7 @@ use super::constants::*;
 use crate::crypto::{SecureRandom, sha256_hmac};
 #[cfg(test)]
 use crate::error::ProxyError;
+use ml_kem::{B32, EncapsulationKey as MlKemEncapsulationKey, Key as MlKemKey, MlKem768};
 use std::time::{SystemTime, UNIX_EPOCH};
 use subtle::ConstantTimeEq;
 use x25519_dalek::{X25519_BASEPOINT_BYTES, x25519};
@@ -105,11 +106,49 @@ mod extension_type {
 /// TLS Cipher Suites
 mod cipher_suite {
     pub const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    pub const TLS_AES_256_GCM_SHA384: [u8; 2] = [0x13, 0x02];
+    pub const TLS_CHACHA20_POLY1305_SHA256: [u8; 2] = [0x13, 0x03];
 }
 
-/// TLS Named Curves
+/// TLS named groups used in KeyShare extensions.
 mod named_curve {
     pub const X25519: u16 = 0x001d;
+    pub const X25519MLKEM768: u16 = 0x11ec;
+}
+
+/// TLS X25519 named group.
+pub(crate) const TLS_NAMED_GROUP_X25519: u16 = named_curve::X25519;
+/// TLS X25519MLKEM768 named group.
+pub(crate) const TLS_NAMED_GROUP_X25519MLKEM768: u16 = named_curve::X25519MLKEM768;
+
+const X25519_KEY_SHARE_LEN: usize = 32;
+const X25519MLKEM768_CLIENT_KEY_SHARE_LEN: usize = 1216;
+const X25519MLKEM768_SERVER_KEY_SHARE_LEN: usize = 1120;
+const MLKEM768_CLIENT_ENCAPSULATION_KEY_LEN: usize = 1184;
+const MLKEM768_SERVER_CIPHERTEXT_LEN: usize = 1088;
+
+/// ServerHello key_share selected for the authenticated ClientHello.
+#[derive(Clone, Debug)]
+pub(crate) struct ServerHelloKeyShare {
+    group: u16,
+    key_exchange: Vec<u8>,
+}
+
+impl ServerHelloKeyShare {
+    pub(crate) fn new(group: u16, key_exchange: Vec<u8>) -> Self {
+        Self {
+            group,
+            key_exchange,
+        }
+    }
+
+    pub(crate) fn group(&self) -> u16 {
+        self.group
+    }
+
+    pub(crate) fn key_exchange(&self) -> &[u8] {
+        &self.key_exchange
+    }
 }
 
 // ============= TLS Validation Result =============
@@ -142,26 +181,28 @@ impl TlsExtensionBuilder {
         }
     }
 
-    /// Add Key Share extension with X25519 key
-    fn add_key_share(&mut self, public_key: &[u8; 32]) -> &mut Self {
+    /// Add KeyShare extension with the selected named group.
+    fn add_key_share(&mut self, group: u16, key_exchange: &[u8]) -> &mut Self {
+        let Ok(key_exchange_len) = u16::try_from(key_exchange.len()) else {
+            return self;
+        };
+        let Some(entry_len) = key_exchange.len().checked_add(4) else {
+            return self;
+        };
+        let Ok(entry_len) = u16::try_from(entry_len) else {
+            return self;
+        };
+
         // Extension type: key_share (0x0033)
         self.extensions
             .extend_from_slice(&extension_type::KEY_SHARE.to_be_bytes());
 
-        // Key share entry: curve (2) + key_len (2) + key (32) = 36 bytes
-        // Extension data length
-        let entry_len: u16 = 2 + 2 + 32; // curve + length + key
+        // ServerHello key_share data is exactly one KeyShareEntry.
         self.extensions.extend_from_slice(&entry_len.to_be_bytes());
-
-        // Named curve: x25519
+        self.extensions.extend_from_slice(&group.to_be_bytes());
         self.extensions
-            .extend_from_slice(&named_curve::X25519.to_be_bytes());
-
-        // Key length
-        self.extensions.extend_from_slice(&(32u16).to_be_bytes());
-
-        // Key data
-        self.extensions.extend_from_slice(public_key);
+            .extend_from_slice(&key_exchange_len.to_be_bytes());
+        self.extensions.extend_from_slice(key_exchange);
 
         self
     }
@@ -230,8 +271,8 @@ impl ServerHelloBuilder {
         }
     }
 
-    fn with_x25519_key(mut self, key: &[u8; 32]) -> Self {
-        self.extensions.add_key_share(key);
+    fn with_key_share(mut self, group: u16, key_exchange: &[u8]) -> Self {
+        self.extensions.add_key_share(group, key_exchange);
         self
     }
 
@@ -241,6 +282,13 @@ impl ServerHelloBuilder {
         self
     }
 
+    fn with_cipher_suite(mut self, cipher_suite: [u8; 2]) -> Self {
+        if cipher_suite != [0, 0] {
+            self.cipher_suite = cipher_suite;
+        }
+        self
+    }
+
     /// Build ServerHello message (without record header)
     fn build_message(&self) -> Vec<u8> {
         let Ok(session_id_len) = u8::try_from(self.session_id.len()) else {
@@ -499,9 +547,137 @@ fn validate_tls_handshake_at_time_with_boot_cap(
 /// Uses RFC 7748 X25519 scalar multiplication over the canonical basepoint,
 /// yielding distribution-consistent public keys for anti-fingerprinting.
 pub fn gen_fake_x25519_key(rng: &SecureRandom) -> [u8; 32] {
-    let mut scalar = [0u8; 32];
-    scalar.copy_from_slice(&rng.bytes(32));
-    x25519(scalar, X25519_BASEPOINT_BYTES)
+    let (_scalar, public_key) = gen_x25519_key_pair(rng);
+    public_key
+}
+
+fn gen_x25519_key_pair(rng: &SecureRandom) -> ([u8; 32], [u8; 32]) {
+    let mut scalar = [0u8; X25519_KEY_SHARE_LEN];
+    rng.fill(&mut scalar);
+    let public_key = x25519(scalar, X25519_BASEPOINT_BYTES);
+    (scalar, public_key)
+}
+
+/// Generate a fake X25519MLKEM768 ServerHello key_share payload.
+pub(crate) fn gen_fake_x25519mlkem768_server_key_share(rng: &SecureRandom) -> Vec<u8> {
+    let mut key_share = vec![0u8; X25519MLKEM768_SERVER_KEY_SHARE_LEN];
+    // FakeTLS never derives TLS traffic secrets from this payload; only the
+    // externally visible named group and vector lengths are protocol-facing.
+    rng.fill(&mut key_share[..MLKEM768_SERVER_CIPHERTEXT_LEN]);
+    let x25519_key = gen_fake_x25519_key(rng);
+    key_share[MLKEM768_SERVER_CIPHERTEXT_LEN..].copy_from_slice(&x25519_key);
+    key_share
+}
+
+fn mlkem768_encapsulate_to_client(client_key: &[u8], rng: &SecureRandom) -> Option<Vec<u8>> {
+    let key_bytes = MlKemKey::<MlKemEncapsulationKey<MlKem768>>::try_from(client_key).ok()?;
+    let encapsulation_key = MlKemEncapsulationKey::<MlKem768>::new(&key_bytes).ok()?;
+    let mut randomness = [0u8; 32];
+    rng.fill(&mut randomness);
+    let randomness = B32::try_from(randomness.as_slice()).ok()?;
+    let (ciphertext, _shared_key) = encapsulation_key.encapsulate_deterministic(&randomness);
+    let ciphertext = ciphertext.as_slice().to_vec();
+    if ciphertext.len() == MLKEM768_SERVER_CIPHERTEXT_LEN {
+        Some(ciphertext)
+    } else {
+        None
+    }
+}
+
+/// Build a valid X25519MLKEM768 ServerHello key_share for the authenticated ClientHello.
+pub(crate) fn build_x25519mlkem768_server_key_share(
+    handshake: &[u8],
+    rng: &SecureRandom,
+) -> Option<Vec<u8>> {
+    let client_key_exchange = client_hello_key_share_group_entry(
+        handshake,
+        TLS_NAMED_GROUP_X25519MLKEM768,
+        X25519MLKEM768_CLIENT_KEY_SHARE_LEN,
+    )?;
+    let client_mlkem_key = client_key_exchange.get(..MLKEM768_CLIENT_ENCAPSULATION_KEY_LEN)?;
+    let client_x25519_key = client_key_exchange.get(MLKEM768_CLIENT_ENCAPSULATION_KEY_LEN..)?;
+    let mlkem_ciphertext = mlkem768_encapsulate_to_client(client_mlkem_key, rng)?;
+
+    let mut client_x25519 = [0u8; X25519_KEY_SHARE_LEN];
+    client_x25519.copy_from_slice(client_x25519_key);
+    let (server_x25519_scalar, server_x25519_key) = gen_x25519_key_pair(rng);
+    let x25519_shared = x25519(server_x25519_scalar, client_x25519);
+    if bool::from(x25519_shared.ct_eq(&[0u8; X25519_KEY_SHARE_LEN])) {
+        return None;
+    }
+
+    let mut key_share = Vec::with_capacity(X25519MLKEM768_SERVER_KEY_SHARE_LEN);
+    key_share.extend_from_slice(&mlkem_ciphertext);
+    key_share.extend_from_slice(&server_x25519_key);
+    Some(key_share)
+}
+
+/// Build a valid X25519 ServerHello key_share for the authenticated ClientHello.
+pub(crate) fn build_x25519_server_key_share(
+    handshake: &[u8],
+    rng: &SecureRandom,
+) -> Option<Vec<u8>> {
+    let client_key_exchange = client_hello_key_share_group_entry(
+        handshake,
+        TLS_NAMED_GROUP_X25519,
+        X25519_KEY_SHARE_LEN,
+    )?;
+    let mut client_x25519 = [0u8; X25519_KEY_SHARE_LEN];
+    client_x25519.copy_from_slice(client_key_exchange);
+    let (server_x25519_scalar, server_x25519_key) = gen_x25519_key_pair(rng);
+    let x25519_shared = x25519(server_x25519_scalar, client_x25519);
+    if bool::from(x25519_shared.ct_eq(&[0u8; X25519_KEY_SHARE_LEN])) {
+        return None;
+    }
+
+    Some(server_x25519_key.to_vec())
+}
+
+fn build_server_hello_key_share_for_group(
+    handshake: &[u8],
+    group: u16,
+    rng: &SecureRandom,
+) -> Option<ServerHelloKeyShare> {
+    let expected_key_exchange_len = client_hello_key_share_group_len(group)?;
+    client_hello_key_share_group_entry(handshake, group, expected_key_exchange_len)?;
+
+    // FakeTLS clients validate ServerHello shape and digest, not TLS traffic
+    // secrets, so the response must mirror the offered group without binding to
+    // the camouflage key bytes embedded in ClientHello.
+    match group {
+        TLS_NAMED_GROUP_X25519MLKEM768 => Some(ServerHelloKeyShare::new(
+            group,
+            gen_fake_x25519mlkem768_server_key_share(rng),
+        )),
+        TLS_NAMED_GROUP_X25519 => Some(ServerHelloKeyShare::new(
+            group,
+            gen_fake_x25519_key(rng).to_vec(),
+        )),
+        _ => None,
+    }
+}
+
+fn server_hello_key_share_candidate_order(preferred_group: Option<u16>) -> [u16; 2] {
+    if preferred_group == Some(TLS_NAMED_GROUP_X25519) {
+        [TLS_NAMED_GROUP_X25519, TLS_NAMED_GROUP_X25519MLKEM768]
+    } else {
+        [TLS_NAMED_GROUP_X25519MLKEM768, TLS_NAMED_GROUP_X25519]
+    }
+}
+
+/// Build a ServerHello key_share using a profile-preferred group when possible.
+pub(crate) fn build_server_hello_key_share(
+    handshake: &[u8],
+    preferred_group: Option<u16>,
+    rng: &SecureRandom,
+) -> Option<ServerHelloKeyShare> {
+    for group in server_hello_key_share_candidate_order(preferred_group) {
+        if let Some(key_share) = build_server_hello_key_share_for_group(handshake, group, rng) {
+            return Some(key_share);
+        }
+    }
+
+    None
 }
 
 /// Build TLS ServerHello response
@@ -520,15 +696,48 @@ pub fn build_server_hello(
     rng: &SecureRandom,
     alpn: Option<Vec<u8>>,
     new_session_tickets: u8,
+) -> Vec<u8> {
+    let server_key_share = ServerHelloKeyShare::new(
+        TLS_NAMED_GROUP_X25519MLKEM768,
+        gen_fake_x25519mlkem768_server_key_share(rng),
+    );
+    build_server_hello_with_cipher(
+        secret,
+        client_digest,
+        session_id,
+        fake_cert_len,
+        rng,
+        cipher_suite::TLS_AES_128_GCM_SHA256,
+        &server_key_share,
+        alpn,
+        new_session_tickets,
+    )
+}
+
+/// Build TLS ServerHello response with a caller-selected cipher suite.
+///
+/// The caller is responsible for selecting a suite that is compatible with the
+/// already-authenticated ClientHello. Keeping the selection outside this
+/// builder avoids extra ClientHello parsing in the response construction path.
+pub(crate) fn build_server_hello_with_cipher(
+    secret: &[u8],
+    client_digest: &[u8; TLS_DIGEST_LEN],
+    session_id: &[u8],
+    fake_cert_len: usize,
+    rng: &SecureRandom,
+    selected_cipher_suite: [u8; 2],
+    server_key_share: &ServerHelloKeyShare,
+    alpn: Option<Vec<u8>>,
+    new_session_tickets: u8,
 ) -> Vec<u8> {
     const MIN_APP_DATA: usize = 64;
     const MAX_APP_DATA: usize = MAX_TLS_CIPHERTEXT_SIZE;
     let fake_cert_len = fake_cert_len.clamp(MIN_APP_DATA, MAX_APP_DATA);
-    let x25519_key = gen_fake_x25519_key(rng);
 
     // Build ServerHello
     let server_hello = ServerHelloBuilder::new(session_id.to_vec())
-        .with_x25519_key(&x25519_key)
+        .with_cipher_suite(selected_cipher_suite)
+        .with_key_share(server_key_share.group(), server_key_share.key_exchange())
         .with_tls13_version()
         .build_record();
 
@@ -538,28 +747,14 @@ pub fn build_server_hello(
         TLS_VERSION[0],
         TLS_VERSION[1],
         0x00,
-        0x01, // length = 1
-        0x01, // CCS byte
+        0x01,
+        0x01,
     ];
 
     // Build first encrypted flight mimic as opaque ApplicationData bytes.
-    // Embed a compact EncryptedExtensions-like ALPN block when selected.
+    // ALPN belongs inside encrypted EncryptedExtensions in real TLS 1.3.
     let mut fake_cert = Vec::with_capacity(fake_cert_len);
-    if let Some(proto) = alpn
-        .as_ref()
-        .filter(|p| !p.is_empty() && p.len() <= u8::MAX as usize)
-    {
-        let proto_list_len = 1usize + proto.len();
-        let ext_data_len = 2usize + proto_list_len;
-        let marker_len = 4usize + ext_data_len;
-        if marker_len <= fake_cert_len {
-            fake_cert.extend_from_slice(&0x0010u16.to_be_bytes());
-            fake_cert.extend_from_slice(&(ext_data_len as u16).to_be_bytes());
-            fake_cert.extend_from_slice(&(proto_list_len as u16).to_be_bytes());
-            fake_cert.push(proto.len() as u8);
-            fake_cert.extend_from_slice(proto);
-        }
-    }
+    let _ = alpn;
     if fake_cert.len() < fake_cert_len {
         fake_cert.extend_from_slice(&rng.bytes(fake_cert_len - fake_cert.len()));
     } else if fake_cert.len() > fake_cert_len {
@@ -580,7 +775,7 @@ pub fn build_server_hello(
     let ticket_count = new_session_tickets.min(4);
     if ticket_count > 0 {
         for _ in 0..ticket_count {
-            let ticket_len: usize = rng.range(48) + 48; // 48-95 bytes
+            let ticket_len: usize = rng.range(48) + 48;
             let mut record = Vec::with_capacity(5 + ticket_len);
             record.push(TLS_RECORD_APPLICATION);
             record.extend_from_slice(&TLS_VERSION);
@@ -927,6 +1122,289 @@ pub fn detect_client_hello_tls_version(handshake: &[u8]) -> Option<ClientHelloTl
     }
 }
 
+fn client_hello_cipher_suites_range(handshake: &[u8]) -> Option<(usize, usize)> {
+    if handshake.len() < 5 || handshake[0] != TLS_RECORD_HANDSHAKE {
+        return None;
+    }
+
+    let record_len = u16::from_be_bytes([handshake[3], handshake[4]]) as usize;
+    let record_end = 5usize.checked_add(record_len)?;
+    if record_end > handshake.len() {
+        return None;
+    }
+
+    let mut pos = 5;
+    if handshake.get(pos) != Some(&0x01) {
+        return None;
+    }
+    pos += 1;
+
+    if pos + 3 > record_end {
+        return None;
+    }
+    let handshake_len = ((handshake[pos] as usize) << 16)
+        | ((handshake[pos + 1] as usize) << 8)
+        | handshake[pos + 2] as usize;
+    pos += 3;
+    let handshake_end = pos.checked_add(handshake_len)?;
+    if handshake_end > record_end {
+        return None;
+    }
+
+    if pos + 2 + 32 > handshake_end {
+        return None;
+    }
+    pos += 2 + 32;
+
+    let session_id_len = *handshake.get(pos)? as usize;
+    pos = pos.checked_add(1)?.checked_add(session_id_len)?;
+    if pos + 2 > handshake_end {
+        return None;
+    }
+
+    let cipher_len = u16::from_be_bytes([handshake[pos], handshake[pos + 1]]) as usize;
+    if cipher_len == 0 || cipher_len % 2 != 0 {
+        return None;
+    }
+    pos += 2;
+    let cipher_end = pos.checked_add(cipher_len)?;
+    if cipher_end > handshake_end {
+        return None;
+    }
+
+    Some((pos, cipher_end))
+}
+
+fn client_hello_extensions_range(handshake: &[u8]) -> Option<(usize, usize)> {
+    if handshake.len() < 5 || handshake[0] != TLS_RECORD_HANDSHAKE {
+        return None;
+    }
+
+    let record_len = u16::from_be_bytes([handshake[3], handshake[4]]) as usize;
+    let record_end = 5usize.checked_add(record_len)?;
+    if record_end > handshake.len() {
+        return None;
+    }
+
+    let mut pos = 5;
+    if handshake.get(pos) != Some(&0x01) {
+        return None;
+    }
+    pos += 1;
+
+    if pos + 3 > record_end {
+        return None;
+    }
+    let handshake_len = ((handshake[pos] as usize) << 16)
+        | ((handshake[pos + 1] as usize) << 8)
+        | handshake[pos + 2] as usize;
+    pos += 3;
+    let handshake_end = pos.checked_add(handshake_len)?;
+    if handshake_end > record_end {
+        return None;
+    }
+
+    if pos + 2 + 32 > handshake_end {
+        return None;
+    }
+    pos += 2 + 32;
+
+    let session_id_len = *handshake.get(pos)? as usize;
+    pos = pos.checked_add(1)?.checked_add(session_id_len)?;
+    if pos + 2 > handshake_end {
+        return None;
+    }
+
+    let cipher_len = u16::from_be_bytes([handshake[pos], handshake[pos + 1]]) as usize;
+    if cipher_len == 0 || cipher_len % 2 != 0 {
+        return None;
+    }
+    pos += 2;
+    pos = pos.checked_add(cipher_len)?;
+    if pos + 1 > handshake_end {
+        return None;
+    }
+
+    let compression_len = *handshake.get(pos)? as usize;
+    pos = pos.checked_add(1)?.checked_add(compression_len)?;
+    if pos == handshake_end {
+        return Some((handshake_end, handshake_end));
+    }
+    if pos + 2 > handshake_end {
+        return None;
+    }
+
+    let extensions_len = u16::from_be_bytes([handshake[pos], handshake[pos + 1]]) as usize;
+    pos += 2;
+    let extensions_end = pos.checked_add(extensions_len)?;
+    if extensions_end > handshake_end {
+        return None;
+    }
+
+    Some((pos, extensions_end))
+}
+
+fn key_share_extension_group_entry<'a>(
+    data: &'a [u8],
+    group: u16,
+    expected_key_exchange_len: usize,
+) -> Option<&'a [u8]> {
+    if data.len() < 2 {
+        return None;
+    }
+
+    let shares_len = u16::from_be_bytes([data[0], data[1]]) as usize;
+    if shares_len != data.len().saturating_sub(2) {
+        return None;
+    }
+
+    let mut pos = 2usize;
+    let shares_end = 2 + shares_len;
+    let mut found_group = None;
+    while pos + 4 <= shares_end {
+        let entry_group = u16::from_be_bytes([data[pos], data[pos + 1]]);
+        let key_exchange_len = u16::from_be_bytes([data[pos + 2], data[pos + 3]]) as usize;
+        pos += 4;
+        let Some(key_exchange_end) = pos.checked_add(key_exchange_len) else {
+            return None;
+        };
+        if key_exchange_end > shares_end {
+            return None;
+        }
+        if entry_group == group {
+            if key_exchange_len != expected_key_exchange_len || found_group.is_some() {
+                return None;
+            }
+            found_group = Some(&data[pos..key_exchange_end]);
+        }
+        pos = key_exchange_end;
+    }
+
+    if pos == shares_end { found_group } else { None }
+}
+
+fn client_hello_key_share_group_entry<'a>(
+    handshake: &'a [u8],
+    group: u16,
+    expected_key_exchange_len: usize,
+) -> Option<&'a [u8]> {
+    let Some((mut pos, extensions_end)) = client_hello_extensions_range(handshake) else {
+        return None;
+    };
+
+    while pos + 4 <= extensions_end {
+        let ext_type = u16::from_be_bytes([handshake[pos], handshake[pos + 1]]);
+        let ext_len = u16::from_be_bytes([handshake[pos + 2], handshake[pos + 3]]) as usize;
+        pos += 4;
+        let Some(ext_end) = pos.checked_add(ext_len) else {
+            return None;
+        };
+        if ext_end > extensions_end {
+            return None;
+        }
+
+        if ext_type == extension_type::KEY_SHARE {
+            return key_share_extension_group_entry(
+                &handshake[pos..ext_end],
+                group,
+                expected_key_exchange_len,
+            );
+        }
+
+        pos = ext_end;
+    }
+
+    None
+}
+
+fn client_hello_offers_cipher_suite(
+    handshake: &[u8],
+    range: (usize, usize),
+    suite: [u8; 2],
+) -> bool {
+    let mut pos = range.0;
+    while pos + 1 < range.1 {
+        if handshake[pos] == suite[0] && handshake[pos + 1] == suite[1] {
+            return true;
+        }
+        pos += 2;
+    }
+    false
+}
+
+fn is_tls13_cipher_suite(suite: [u8; 2]) -> bool {
+    suite == cipher_suite::TLS_AES_128_GCM_SHA256
+        || suite == cipher_suite::TLS_AES_256_GCM_SHA384
+        || suite == cipher_suite::TLS_CHACHA20_POLY1305_SHA256
+}
+
+/// Select the ServerHello cipher suite from the already-received ClientHello.
+///
+/// This is intentionally a borrowed, zero-allocation scan. It runs only for an
+/// authenticated success response and fails closed for malformed or unsupported
+/// ClientHello shapes that cannot produce a DPI-consistent ServerHello.
+pub(crate) fn select_server_hello_cipher_suite(
+    handshake: &[u8],
+    preferred: [u8; 2],
+) -> Option<[u8; 2]> {
+    let preferred = if is_tls13_cipher_suite(preferred) {
+        preferred
+    } else {
+        cipher_suite::TLS_AES_128_GCM_SHA256
+    };
+    let Some(range) = client_hello_cipher_suites_range(handshake) else {
+        return None;
+    };
+
+    if client_hello_offers_cipher_suite(handshake, range, preferred) {
+        return Some(preferred);
+    }
+
+    for fallback in [
+        cipher_suite::TLS_AES_128_GCM_SHA256,
+        cipher_suite::TLS_CHACHA20_POLY1305_SHA256,
+        cipher_suite::TLS_AES_256_GCM_SHA384,
+    ] {
+        if client_hello_offers_cipher_suite(handshake, range, fallback) {
+            return Some(fallback);
+        }
+    }
+
+    None
+}
+
+fn client_hello_key_share_group_len(group: u16) -> Option<usize> {
+    match group {
+        TLS_NAMED_GROUP_X25519MLKEM768 => Some(X25519MLKEM768_CLIENT_KEY_SHARE_LEN),
+        TLS_NAMED_GROUP_X25519 => Some(X25519_KEY_SHARE_LEN),
+        _ => None,
+    }
+}
+
+/// Select the ServerHello key_share named group from the authenticated ClientHello.
+///
+/// Malformed key_share structures fail closed so authenticated but
+/// DPI-inconsistent ClientHellos take the ordinary masking fallback path.
+pub(crate) fn select_server_hello_key_share_group(handshake: &[u8]) -> Option<u16> {
+    select_server_hello_key_share_group_with_preference(handshake, None)
+}
+
+/// Select the ServerHello key_share named group with an origin-profile preference.
+pub(crate) fn select_server_hello_key_share_group_with_preference(
+    handshake: &[u8],
+    preferred_group: Option<u16>,
+) -> Option<u16> {
+    for group in server_hello_key_share_candidate_order(preferred_group) {
+        let expected_key_exchange_len = client_hello_key_share_group_len(group)?;
+        if client_hello_key_share_group_entry(handshake, group, expected_key_exchange_len).is_some()
+        {
+            return Some(group);
+        }
+    }
+
+    None
+}
+
 /// Check if bytes look like a TLS ClientHello
 pub fn is_tls_handshake(first_bytes: &[u8]) -> bool {
     if first_bytes.len() < 3 {

src/protocol/tls_fingerprint.rs

@@ -0,0 +1,450 @@
+//! Passive JA3 / JA4 TLS ClientHello fingerprinting.
+
+use crate::crypto::hash::md5;
+use crate::crypto::sha256;
+use crate::protocol::constants::TLS_RECORD_HANDSHAKE;
+
+const EXT_SNI: u16 = 0x0000;
+const EXT_SUPPORTED_GROUPS: u16 = 0x000a;
+const EXT_EC_POINT_FORMATS: u16 = 0x000b;
+const EXT_SIGNATURE_ALGORITHMS: u16 = 0x000d;
+const EXT_ALPN: u16 = 0x0010;
+const EXT_SUPPORTED_VERSIONS: u16 = 0x002b;
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct TlsClientFingerprint {
+    pub ja3: String,
+    pub ja3_raw: String,
+    pub ja4: String,
+    pub ja4_raw: String,
+}
+
+#[derive(Default)]
+struct ParsedClientHello {
+    legacy_version: u16,
+    ciphers: Vec<u16>,
+    extensions: Vec<u16>,
+    supported_groups: Vec<u16>,
+    ec_point_formats: Vec<u8>,
+    signature_algorithms: Vec<u16>,
+    supported_versions: Vec<u16>,
+    alpn_first: Option<Vec<u8>>,
+    sni_present: bool,
+}
+
+pub fn fingerprint_client_hello(handshake: &[u8]) -> Option<TlsClientFingerprint> {
+    let parsed = parse_client_hello(handshake)?;
+    let ja3_raw = ja3_raw(&parsed);
+    let ja3 = hex::encode(md5(ja3_raw.as_bytes()));
+    let (ja4, ja4_raw) = ja4(&parsed);
+
+    Some(TlsClientFingerprint {
+        ja3,
+        ja3_raw,
+        ja4,
+        ja4_raw,
+    })
+}
+
+fn parse_client_hello(handshake: &[u8]) -> Option<ParsedClientHello> {
+    if handshake.len() < 5 || handshake[0] != TLS_RECORD_HANDSHAKE {
+        return None;
+    }
+
+    let record_len = read_u16_at(handshake, 3)? as usize;
+    let record_end = 5usize.checked_add(record_len)?;
+    if record_end > handshake.len() {
+        return None;
+    }
+
+    let mut pos = 5usize;
+    if *handshake.get(pos)? != 0x01 {
+        return None;
+    }
+    pos = pos.checked_add(1)?;
+
+    if pos + 3 > record_end {
+        return None;
+    }
+    let handshake_len = ((usize::from(handshake[pos])) << 16)
+        | ((usize::from(handshake[pos + 1])) << 8)
+        | usize::from(handshake[pos + 2]);
+    pos = pos.checked_add(3)?;
+    let handshake_end = pos.checked_add(handshake_len)?;
+    if handshake_end > record_end {
+        return None;
+    }
+
+    if pos + 2 + 32 > handshake_end {
+        return None;
+    }
+    let legacy_version = read_u16_at(handshake, pos)?;
+    pos = pos.checked_add(2 + 32)?;
+
+    let session_id_len = usize::from(*handshake.get(pos)?);
+    pos = pos.checked_add(1)?.checked_add(session_id_len)?;
+    if pos + 2 > handshake_end {
+        return None;
+    }
+
+    let cipher_len = read_u16_at(handshake, pos)? as usize;
+    pos = pos.checked_add(2)?;
+    let cipher_end = pos.checked_add(cipher_len)?;
+    if cipher_end > handshake_end || cipher_len % 2 != 0 {
+        return None;
+    }
+    let mut ciphers = Vec::with_capacity(cipher_len / 2);
+    while pos + 1 < cipher_end {
+        let value = read_u16_at(handshake, pos)?;
+        if !is_grease(value) {
+            ciphers.push(value);
+        }
+        pos = pos.checked_add(2)?;
+    }
+
+    let comp_len = usize::from(*handshake.get(pos)?);
+    pos = pos.checked_add(1)?.checked_add(comp_len)?;
+    if pos > handshake_end {
+        return None;
+    }
+
+    let mut parsed = ParsedClientHello {
+        legacy_version,
+        ciphers,
+        ..ParsedClientHello::default()
+    };
+
+    if pos == handshake_end {
+        return Some(parsed);
+    }
+    if pos + 2 > handshake_end {
+        return None;
+    }
+
+    let ext_len = read_u16_at(handshake, pos)? as usize;
+    pos = pos.checked_add(2)?;
+    let ext_end = pos.checked_add(ext_len)?;
+    if ext_end > handshake_end {
+        return None;
+    }
+
+    while pos + 4 <= ext_end {
+        let etype = read_u16_at(handshake, pos)?;
+        let elen = read_u16_at(handshake, pos + 2)? as usize;
+        pos = pos.checked_add(4)?;
+        let data_end = pos.checked_add(elen)?;
+        if data_end > ext_end {
+            return None;
+        }
+        let data = handshake.get(pos..data_end)?;
+
+        if !is_grease(etype) {
+            parsed.extensions.push(etype);
+            match etype {
+                EXT_SNI => parsed.sni_present = true,
+                EXT_SUPPORTED_GROUPS => {
+                    parsed.supported_groups = parse_u16_vector(data, 2)?;
+                }
+                EXT_EC_POINT_FORMATS => {
+                    parsed.ec_point_formats = parse_u8_vector(data)?;
+                }
+                EXT_SIGNATURE_ALGORITHMS => {
+                    parsed.signature_algorithms = parse_u16_vector(data, 2)?;
+                }
+                EXT_ALPN => {
+                    parsed.alpn_first = parse_alpn_first(data)?;
+                }
+                EXT_SUPPORTED_VERSIONS => {
+                    parsed.supported_versions = parse_u16_vector(data, 1)?;
+                }
+                _ => {}
+            }
+        }
+
+        pos = data_end;
+    }
+
+    if pos != ext_end {
+        return None;
+    }
+
+    Some(parsed)
+}
+
+fn parse_u16_vector(data: &[u8], len_prefix_len: usize) -> Option<Vec<u16>> {
+    let (list_len, mut pos) = match len_prefix_len {
+        1 => (usize::from(*data.first()?), 1usize),
+        2 => (read_u16_at(data, 0)? as usize, 2usize),
+        _ => return None,
+    };
+    let list_end = pos.checked_add(list_len)?;
+    if list_end > data.len() || list_len % 2 != 0 {
+        return None;
+    }
+
+    let mut out = Vec::with_capacity(list_len / 2);
+    while pos + 1 < list_end {
+        let value = read_u16_at(data, pos)?;
+        if !is_grease(value) {
+            out.push(value);
+        }
+        pos = pos.checked_add(2)?;
+    }
+    Some(out)
+}
+
+fn parse_u8_vector(data: &[u8]) -> Option<Vec<u8>> {
+    let list_len = usize::from(*data.first()?);
+    let list_start = 1usize;
+    let list_end = list_start.checked_add(list_len)?;
+    if list_end > data.len() {
+        return None;
+    }
+    Some(data.get(list_start..list_end)?.to_vec())
+}
+
+fn parse_alpn_first(data: &[u8]) -> Option<Option<Vec<u8>>> {
+    if data.len() < 2 {
+        return None;
+    }
+    let list_len = read_u16_at(data, 0)? as usize;
+    let mut pos = 2usize;
+    let list_end = pos.checked_add(list_len)?;
+    if list_end > data.len() {
+        return None;
+    }
+    if pos == list_end {
+        return Some(None);
+    }
+
+    let protocol_len = usize::from(*data.get(pos)?);
+    pos = pos.checked_add(1)?;
+    let protocol_end = pos.checked_add(protocol_len)?;
+    if protocol_end > list_end {
+        return None;
+    }
+    if protocol_len == 0 {
+        return Some(None);
+    }
+    Some(Some(data.get(pos..protocol_end)?.to_vec()))
+}
+
+fn ja3_raw(parsed: &ParsedClientHello) -> String {
+    format!(
+        "{},{},{},{},{}",
+        parsed.legacy_version,
+        join_decimal_u16(&parsed.ciphers),
+        join_decimal_u16(&parsed.extensions),
+        join_decimal_u16(&parsed.supported_groups),
+        join_decimal_u8(&parsed.ec_point_formats)
+    )
+}
+
+fn ja4(parsed: &ParsedClientHello) -> (String, String) {
+    let a = format!(
+        "t{}{}{:02}{:02}{}",
+        ja4_version_code(parsed),
+        if parsed.sni_present { "d" } else { "i" },
+        count_ja4(parsed.ciphers.len()),
+        count_ja4(parsed.extensions.len()),
+        ja4_alpn_marker(parsed.alpn_first.as_deref())
+    );
+
+    let mut ciphers = parsed.ciphers.clone();
+    ciphers.sort_unstable();
+    let cipher_raw = join_hex_u16(&ciphers);
+    let cipher_hash = if ciphers.is_empty() {
+        "000000000000".to_string()
+    } else {
+        sha256_truncated_12(&cipher_raw)
+    };
+
+    let mut extensions_for_hash = parsed
+        .extensions
+        .iter()
+        .copied()
+        .filter(|value| *value != EXT_SNI && *value != EXT_ALPN)
+        .collect::<Vec<_>>();
+    extensions_for_hash.sort_unstable();
+    let extension_raw = join_hex_u16(&extensions_for_hash);
+    let signature_raw = join_hex_u16(&parsed.signature_algorithms);
+    let extension_hash_input = if signature_raw.is_empty() {
+        extension_raw.clone()
+    } else {
+        format!("{extension_raw}_{signature_raw}")
+    };
+    let extension_hash = if extensions_for_hash.is_empty() {
+        "000000000000".to_string()
+    } else {
+        sha256_truncated_12(&extension_hash_input)
+    };
+
+    (
+        format!("{a}_{cipher_hash}_{extension_hash}"),
+        format!("{a}_{cipher_raw}_{extension_hash_input}"),
+    )
+}
+
+fn ja4_version_code(parsed: &ParsedClientHello) -> &'static str {
+    let version = parsed
+        .supported_versions
+        .iter()
+        .copied()
+        .max()
+        .unwrap_or(parsed.legacy_version);
+    match version {
+        0x0304 => "13",
+        0x0303 => "12",
+        0x0302 => "11",
+        0x0301 => "10",
+        0x0300 => "s3",
+        0x0002 => "s2",
+        0xfeff => "d1",
+        0xfefd => "d2",
+        0xfefc => "d3",
+        _ => "00",
+    }
+}
+
+fn ja4_alpn_marker(alpn_first: Option<&[u8]>) -> String {
+    let Some(value) = alpn_first else {
+        return "00".to_string();
+    };
+    let Some(first) = value.first().copied() else {
+        return "00".to_string();
+    };
+    let last = value.last().copied().unwrap_or(first);
+    if first.is_ascii_alphanumeric() && last.is_ascii_alphanumeric() {
+        return format!("{}{}", first as char, last as char);
+    }
+
+    let encoded = hex::encode(value);
+    if encoded.is_empty() {
+        return "00".to_string();
+    }
+    let first_hex = encoded.as_bytes()[0] as char;
+    let last_hex = encoded.as_bytes()[encoded.len().saturating_sub(1)] as char;
+    format!("{first_hex}{last_hex}")
+}
+
+fn count_ja4(count: usize) -> usize {
+    count.min(99)
+}
+
+fn sha256_truncated_12(input: &str) -> String {
+    let mut encoded = hex::encode(sha256(input.as_bytes()));
+    encoded.truncate(12);
+    encoded
+}
+
+fn join_decimal_u16(values: &[u16]) -> String {
+    values
+        .iter()
+        .map(u16::to_string)
+        .collect::<Vec<_>>()
+        .join("-")
+}
+
+fn join_decimal_u8(values: &[u8]) -> String {
+    values
+        .iter()
+        .map(u8::to_string)
+        .collect::<Vec<_>>()
+        .join("-")
+}
+
+fn join_hex_u16(values: &[u16]) -> String {
+    values
+        .iter()
+        .map(|value| format!("{value:04x}"))
+        .collect::<Vec<_>>()
+        .join(",")
+}
+
+fn read_u16_at(buf: &[u8], pos: usize) -> Option<u16> {
+    Some(u16::from_be_bytes([
+        *buf.get(pos)?,
+        *buf.get(pos.checked_add(1)?)?,
+    ]))
+}
+
+fn is_grease(value: u16) -> bool {
+    let high = (value >> 8) as u8;
+    let low = value as u8;
+    high == low && (high & 0x0f) == 0x0a
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn sample_client_hello() -> Vec<u8> {
+        let mut body = Vec::new();
+        body.extend_from_slice(&[0x03, 0x03]);
+        body.extend_from_slice(&[0x11; 32]);
+        body.push(0);
+        body.extend_from_slice(&10u16.to_be_bytes());
+        body.extend_from_slice(&[0x0a, 0x0a, 0x13, 0x01, 0x13, 0x02, 0xc0, 0x2f, 0x00, 0xff]);
+        body.push(1);
+        body.push(0);
+
+        let mut extensions = Vec::new();
+        append_ext(&mut extensions, EXT_SNI, &[0, 0]);
+        append_ext(&mut extensions, EXT_ALPN, &[0, 3, 2, b'h', b'2']);
+        append_ext(
+            &mut extensions,
+            EXT_SUPPORTED_GROUPS,
+            &[0, 6, 0x0a, 0x0a, 0x00, 0x17, 0x00, 0x1d],
+        );
+        append_ext(&mut extensions, EXT_EC_POINT_FORMATS, &[1, 0]);
+        append_ext(
+            &mut extensions,
+            EXT_SIGNATURE_ALGORITHMS,
+            &[0, 4, 0x04, 0x03, 0x08, 0x04],
+        );
+        append_ext(
+            &mut extensions,
+            EXT_SUPPORTED_VERSIONS,
+            &[4, 0x03, 0x04, 0x03, 0x03],
+        );
+        body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+        body.extend_from_slice(&extensions);
+
+        let mut record = Vec::new();
+        record.push(TLS_RECORD_HANDSHAKE);
+        record.extend_from_slice(&[0x03, 0x01]);
+        record.extend_from_slice(&((body.len() + 4) as u16).to_be_bytes());
+        record.push(0x01);
+        record.extend_from_slice(&[
+            ((body.len() >> 16) & 0xff) as u8,
+            ((body.len() >> 8) & 0xff) as u8,
+            (body.len() & 0xff) as u8,
+        ]);
+        record.extend_from_slice(&body);
+        record
+    }
+
+    fn append_ext(out: &mut Vec<u8>, etype: u16, data: &[u8]) {
+        out.extend_from_slice(&etype.to_be_bytes());
+        out.extend_from_slice(&(data.len() as u16).to_be_bytes());
+        out.extend_from_slice(data);
+    }
+
+    #[test]
+    fn ja3_and_ja4_ignore_grease_and_remain_stable() {
+        let fp = fingerprint_client_hello(&sample_client_hello())
+            .expect("sample ClientHello must fingerprint");
+        assert_eq!(
+            fp.ja3_raw,
+            "771,4865-4866-49199-255,0-16-10-11-13-43,23-29,0"
+        );
+        assert!(fp.ja4.starts_with("t13d0406h2_"));
+    }
+
+    #[test]
+    fn malformed_client_hello_returns_none() {
+        let mut hello = sample_client_hello();
+        hello.truncate(12);
+        assert!(fingerprint_client_hello(&hello).is_none());
+    }
+}

src/proxy/client.rs

@@ -98,6 +98,7 @@ use crate::error::{HandshakeResult, ProxyError, Result, StreamError};
 use crate::ip_tracker::UserIpTracker;
 use crate::protocol::constants::*;
 use crate::protocol::tls;
+use crate::protocol::tls_fingerprint::{self, TlsClientFingerprint};
 use crate::stats::beobachten::BeobachtenStore;
 use crate::stats::{ReplayChecker, Stats};
 use crate::stream::{BufferPool, CryptoReader, CryptoWriter};
@@ -112,7 +113,7 @@ use crate::proxy::handshake::{
 };
 #[cfg(test)]
 use crate::proxy::handshake::{handle_mtproto_handshake, handle_tls_handshake};
-use crate::proxy::masking::handle_bad_client;
+use crate::proxy::masking::handle_bad_client_with_shared;
 use crate::proxy::middle_relay::handle_via_middle_proxy;
 use crate::proxy::route_mode::{RelayRouteMode, RouteRuntimeController};
 use crate::proxy::shared_state::ProxySharedState;
@@ -309,6 +310,7 @@ fn masking_outcome<R, W>(
     local_addr: SocketAddr,
     config: Arc<ProxyConfig>,
     beobachten: Arc<BeobachtenStore>,
+    shared: Arc<ProxySharedState>,
 ) -> HandshakeOutcome
 where
     R: AsyncRead + Unpin + Send + 'static,
@@ -324,7 +326,7 @@ where
         )
         .await;
 
-        handle_bad_client(
+        handle_bad_client_with_shared(
             reader,
             writer,
             &initial_data,
@@ -332,6 +334,7 @@ where
             local_addr,
             &config,
             &beobachten,
+            shared.as_ref(),
         )
         .await;
         Ok(())
@@ -350,6 +353,60 @@ fn record_beobachten_class(
     beobachten.record(class, peer_ip, beobachten_ttl(config));
 }
 
+fn tls_fingerprint_collection_enabled(config: &ProxyConfig) -> bool {
+    config.general.beobachten || config.server.api.runtime_edge_enabled
+}
+
+fn observe_tls_client_fingerprint(
+    stats: &Stats,
+    config: &ProxyConfig,
+    peer_ip: IpAddr,
+    handshake: &[u8],
+) -> Option<TlsClientFingerprint> {
+    if !tls_fingerprint_collection_enabled(config) {
+        return None;
+    }
+
+    match tls_fingerprint::fingerprint_client_hello(handshake) {
+        Some(fingerprint) => {
+            stats.record_tls_fingerprint_observed(&fingerprint, peer_ip, beobachten_ttl(config));
+            Some(fingerprint)
+        }
+        None => {
+            stats.increment_tls_fingerprint_parse_error();
+            None
+        }
+    }
+}
+
+fn record_tls_fingerprint_auth_success(
+    stats: &Stats,
+    config: &ProxyConfig,
+    peer_ip: IpAddr,
+    fingerprint: Option<&TlsClientFingerprint>,
+    user: &str,
+) {
+    if let Some(fingerprint) = fingerprint {
+        stats.record_tls_fingerprint_auth_success(
+            fingerprint,
+            peer_ip,
+            user,
+            beobachten_ttl(config),
+        );
+    }
+}
+
+fn record_tls_fingerprint_bad_or_probe(
+    stats: &Stats,
+    config: &ProxyConfig,
+    peer_ip: IpAddr,
+    fingerprint: Option<&TlsClientFingerprint>,
+) {
+    if let Some(fingerprint) = fingerprint {
+        stats.record_tls_fingerprint_bad_or_probe(fingerprint, peer_ip, beobachten_ttl(config));
+    }
+}
+
 fn classify_expected_64_got_0(kind: std::io::ErrorKind) -> Option<&'static str> {
     match kind {
         std::io::ErrorKind::UnexpectedEof => Some("expected_64_got_0_unexpected_eof"),
@@ -663,6 +720,7 @@ where
                     local_addr,
                     config.clone(),
                     beobachten.clone(),
+                    shared.clone(),
                 ));
             }
 
@@ -684,6 +742,7 @@ where
                         local_addr,
                         config.clone(),
                         beobachten.clone(),
+                        shared.clone(),
                     ));
                 }
             };
@@ -702,9 +761,13 @@ where
                     local_addr,
                     config.clone(),
                     beobachten.clone(),
+                    shared.clone(),
                 ));
             }
 
+            let tls_fingerprint =
+                observe_tls_client_fingerprint(stats.as_ref(), &config, real_peer.ip(), &handshake);
+
             let (read_half, write_half) = tokio::io::split(stream);
 
             let (mut tls_reader, tls_writer, tls_user) = match handle_tls_handshake_with_shared(
@@ -715,6 +778,12 @@ where
                 HandshakeResult::Success(result) => result,
                 HandshakeResult::BadClient { reader, writer } => {
                     stats.increment_connects_bad_with_class("tls_handshake_bad_client");
+                    record_tls_fingerprint_bad_or_probe(
+                        stats.as_ref(),
+                        &config,
+                        real_peer.ip(),
+                        tls_fingerprint.as_ref(),
+                    );
                     return Ok(masking_outcome(
                         reader,
                         writer,
@@ -723,13 +792,27 @@ where
                         local_addr,
                         config.clone(),
                         beobachten.clone(),
+                        shared.clone(),
                     ));
                 }
                 HandshakeResult::Error(e) => {
+                    record_tls_fingerprint_bad_or_probe(
+                        stats.as_ref(),
+                        &config,
+                        real_peer.ip(),
+                        tls_fingerprint.as_ref(),
+                    );
                     increment_bad_on_unknown_tls_sni(stats.as_ref(), &e);
                     return Err(e);
                 }
             };
+            record_tls_fingerprint_auth_success(
+                stats.as_ref(),
+                &config,
+                real_peer.ip(),
+                tls_fingerprint.as_ref(),
+                tls_user.as_str(),
+            );
 
             debug!(peer = %peer, "Reading MTProto handshake through TLS");
             let mtproto_data = tls_reader.read_exact(HANDSHAKE_LEN).await?;
@@ -767,6 +850,7 @@ where
                         local_addr,
                         config.clone(),
                         beobachten.clone(),
+                        shared.clone(),
                     ));
                 }
                 HandshakeResult::Error(e) => return Err(e),
@@ -796,6 +880,7 @@ where
                     local_addr,
                     config.clone(),
                     beobachten.clone(),
+                    shared.clone(),
                 ));
             }
 
@@ -821,6 +906,7 @@ where
                         local_addr,
                         config.clone(),
                         beobachten.clone(),
+                        shared.clone(),
                     ));
                 }
                 HandshakeResult::Error(e) => return Err(e),
@@ -1252,6 +1338,7 @@ impl RunningClientHandler {
                 local_addr,
                 self.config.clone(),
                 self.beobachten.clone(),
+                self.shared.clone(),
             ));
         }
 
@@ -1273,6 +1360,7 @@ impl RunningClientHandler {
                     local_addr,
                     self.config.clone(),
                     self.beobachten.clone(),
+                    self.shared.clone(),
                 ));
             }
         };
@@ -1292,9 +1380,17 @@ impl RunningClientHandler {
                 local_addr,
                 self.config.clone(),
                 self.beobachten.clone(),
+                self.shared.clone(),
             ));
         }
 
+        let tls_fingerprint = observe_tls_client_fingerprint(
+            self.stats.as_ref(),
+            &self.config,
+            peer.ip(),
+            &handshake,
+        );
+
         let config = self.config.clone();
         let replay_checker = self.replay_checker.clone();
         let stats = self.stats.clone();
@@ -1318,6 +1414,12 @@ impl RunningClientHandler {
             HandshakeResult::Success(result) => result,
             HandshakeResult::BadClient { reader, writer } => {
                 stats.increment_connects_bad_with_class("tls_handshake_bad_client");
+                record_tls_fingerprint_bad_or_probe(
+                    stats.as_ref(),
+                    &config,
+                    peer.ip(),
+                    tls_fingerprint.as_ref(),
+                );
                 return Ok(masking_outcome(
                     reader,
                     writer,
@@ -1326,13 +1428,27 @@ impl RunningClientHandler {
                     local_addr,
                     config.clone(),
                     self.beobachten.clone(),
+                    self.shared.clone(),
                 ));
             }
             HandshakeResult::Error(e) => {
+                record_tls_fingerprint_bad_or_probe(
+                    stats.as_ref(),
+                    &config,
+                    peer.ip(),
+                    tls_fingerprint.as_ref(),
+                );
                 increment_bad_on_unknown_tls_sni(stats.as_ref(), &e);
                 return Err(e);
             }
         };
+        record_tls_fingerprint_auth_success(
+            stats.as_ref(),
+            &config,
+            peer.ip(),
+            tls_fingerprint.as_ref(),
+            tls_user.as_str(),
+        );
 
         debug!(peer = %peer, "Reading MTProto handshake through TLS");
         let mtproto_data = tls_reader.read_exact(HANDSHAKE_LEN).await?;
@@ -1380,6 +1496,7 @@ impl RunningClientHandler {
                     local_addr,
                     config.clone(),
                     self.beobachten.clone(),
+                    self.shared.clone(),
                 ));
             }
             HandshakeResult::Error(e) => return Err(e),
@@ -1427,6 +1544,7 @@ impl RunningClientHandler {
                 local_addr,
                 self.config.clone(),
                 self.beobachten.clone(),
+                self.shared.clone(),
             ));
         }
 
@@ -1465,6 +1583,7 @@ impl RunningClientHandler {
                     local_addr,
                     config.clone(),
                     self.beobachten.clone(),
+                    self.shared.clone(),
                 ));
             }
             HandshakeResult::Error(e) => return Err(e),
@@ -1558,6 +1677,11 @@ impl RunningClientHandler {
     {
         let user = success.user.clone();
 
+        if !shared.is_user_enabled(&user) {
+            warn!(user = %user, "Disabled user rejected");
+            return Err(ProxyError::UserDisabled { user });
+        }
+
         let user_limit_reservation = match Self::acquire_user_connection_reservation_static(
             &user,
             &config,
@@ -1576,6 +1700,8 @@ impl RunningClientHandler {
 
         let route_snapshot = route_runtime.snapshot();
         let session_id = rng.u64();
+        let _user_session = shared.register_user_session(&user, session_id);
+        let session_cancel = _user_session.token();
         let selected_me_pool = if config.general.use_middle_proxy
             && matches!(route_snapshot.mode, RelayRouteMode::Middle)
         {
@@ -1607,6 +1733,7 @@ impl RunningClientHandler {
                     route_runtime.subscribe(),
                     route_snapshot,
                     session_id,
+                    session_cancel.clone(),
                     shared.clone(),
                 )
                 .await
@@ -1625,6 +1752,7 @@ impl RunningClientHandler {
                     route_snapshot,
                     session_id,
                     local_addr,
+                    session_cancel.clone(),
                     shared.clone(),
                 )
                 .await
@@ -1644,6 +1772,7 @@ impl RunningClientHandler {
                 route_snapshot,
                 session_id,
                 local_addr,
+                session_cancel,
                 shared.clone(),
             )
             .await

src/proxy/direct_relay.rs

@@ -10,6 +10,7 @@ use std::time::Duration;
 
 use tokio::io::{AsyncRead, AsyncWrite, AsyncWriteExt, ReadHalf, WriteHalf, split};
 use tokio::sync::watch;
+use tokio_util::sync::CancellationToken;
 use tracing::{debug, info, warn};
 
 use crate::config::ProxyConfig;
@@ -258,6 +259,7 @@ where
         route_snapshot,
         session_id,
         SocketAddr::from(([0, 0, 0, 0], config.server.port)),
+        CancellationToken::new(),
         ProxySharedState::new(),
     )
     .await
@@ -276,6 +278,7 @@ pub(crate) async fn handle_via_direct_with_shared<R, W>(
     route_snapshot: RouteCutoverState,
     session_id: u64,
     local_addr: SocketAddr,
+    session_cancel: CancellationToken,
     shared: Arc<ProxySharedState>,
 ) -> Result<()>
 where
@@ -302,14 +305,25 @@ where
             "Ignoring invalid scope hint and falling back to default upstream selection"
         );
     }
-    let tg_stream = upstream_manager
-        .connect(dc_addr, Some(success.dc_idx), scope_hint)
-        .await?;
+    let tg_stream = tokio::select! {
+        result = upstream_manager.connect(dc_addr, Some(success.dc_idx), scope_hint) => result?,
+        _ = session_cancel.cancelled() => {
+            return Err(ProxyError::UserDisabled {
+                user: user.to_string(),
+            });
+        }
+    };
 
     debug!(peer = %success.peer, dc_addr = %dc_addr, "Connected, performing TG handshake");
 
-    let (tg_reader, tg_writer) =
-        do_tg_handshake_static(tg_stream, &success, &config, rng.as_ref()).await?;
+    let (tg_reader, tg_writer) = tokio::select! {
+        result = do_tg_handshake_static(tg_stream, &success, &config, rng.as_ref()) => result?,
+        _ = session_cancel.cancelled() => {
+            return Err(ProxyError::UserDisabled {
+                user: user.to_string(),
+            });
+        }
+    };
 
     debug!(peer = %success.peer, "TG handshake complete, starting relay");
 
@@ -331,20 +345,22 @@ where
     } else {
         Duration::from_secs(1800)
     };
-    let relay_result = crate::proxy::relay::relay_bidirectional_with_activity_timeout_and_lease(
-        client_reader,
-        client_writer,
-        tg_reader,
-        tg_writer,
-        config.general.direct_relay_copy_buf_c2s_bytes,
-        config.general.direct_relay_copy_buf_s2c_bytes,
-        user,
-        Arc::clone(&stats),
-        config.access.user_data_quota.get(user).copied(),
-        buffer_pool,
-        traffic_lease,
-        relay_activity_timeout,
-    );
+    let relay_result =
+        crate::proxy::relay::relay_bidirectional_with_activity_timeout_lease_and_cancel(
+            client_reader,
+            client_writer,
+            tg_reader,
+            tg_writer,
+            config.general.direct_relay_copy_buf_c2s_bytes,
+            config.general.direct_relay_copy_buf_s2c_bytes,
+            user,
+            Arc::clone(&stats),
+            config.access.user_data_quota.get(user).copied(),
+            buffer_pool,
+            traffic_lease,
+            relay_activity_timeout,
+            session_cancel.clone(),
+        );
     tokio::pin!(relay_result);
     let relay_result = loop {
         if let Some(cutover) =
@@ -371,6 +387,11 @@ where
                     break relay_result.await;
                 }
             }
+            _ = session_cancel.cancelled() => {
+                break Err(ProxyError::UserDisabled {
+                    user: user.to_string(),
+                });
+            }
         }
     };
 

src/proxy/handshake.rs

@@ -4,7 +4,6 @@
 
 use dashmap::DashMap;
 use dashmap::mapref::entry::Entry;
-use hmac::{Hmac, Mac};
 #[cfg(test)]
 use std::collections::HashSet;
 use std::collections::hash_map::DefaultHasher;
@@ -33,8 +32,10 @@ use crate::stream::{CryptoReader, CryptoWriter, FakeTlsReader, FakeTlsWriter};
 use crate::tls_front::{TlsFrontCache, emulator};
 #[cfg(test)]
 use rand::RngExt;
-use sha2::Sha256;
-use subtle::ConstantTimeEq;
+
+mod tls_auth;
+
+use self::tls_auth::{parse_tls_auth_material, validate_tls_secret_candidate};
 
 const ACCESS_SECRET_BYTES: usize = 16;
 const UNKNOWN_SNI_WARN_COOLDOWN_SECS: u64 = 5;
@@ -58,8 +59,6 @@ const OVERLOAD_CANDIDATE_BUDGET_UNHINTED: usize = 8;
 const EXPENSIVE_INVALID_SCAN_SATURATION_THRESHOLD: usize = 64;
 const RECENT_USER_RING_SCAN_LIMIT: usize = 32;
 
-type HmacSha256 = Hmac<Sha256>;
-
 #[cfg(test)]
 const AUTH_PROBE_BACKOFF_BASE_MS: u64 = 1;
 #[cfg(not(test))]
@@ -104,23 +103,6 @@ fn should_emit_unknown_sni_warn_in(shared: &ProxySharedState, now: Instant) -> b
     true
 }
 
-#[derive(Clone, Copy)]
-struct ParsedTlsAuthMaterial {
-    digest: [u8; tls::TLS_DIGEST_LEN],
-    session_id: [u8; 32],
-    session_id_len: usize,
-    now: i64,
-    ignore_time_skew: bool,
-    boot_time_cap_secs: u32,
-}
-
-#[derive(Clone, Copy)]
-struct TlsCandidateValidation {
-    digest: [u8; tls::TLS_DIGEST_LEN],
-    session_id: [u8; 32],
-    session_id_len: usize,
-}
-
 struct MtprotoCandidateValidation {
     proto_tag: ProtoTag,
     dc_idx: i16,
@@ -251,104 +233,6 @@ fn budget_for_validation(total_users: usize, overload: bool, has_hint: bool) ->
     total_users.min(cap.max(1))
 }
 
-fn parse_tls_auth_material(
-    handshake: &[u8],
-    ignore_time_skew: bool,
-    replay_window_secs: u64,
-) -> Option<ParsedTlsAuthMaterial> {
-    if handshake.len() < tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN + 1 {
-        return None;
-    }
-
-    let digest: [u8; tls::TLS_DIGEST_LEN] = handshake
-        [tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN]
-        .try_into()
-        .ok()?;
-
-    let session_id_len_pos = tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN;
-    let session_id_len = usize::from(handshake.get(session_id_len_pos).copied()?);
-    if session_id_len > 32 {
-        return None;
-    }
-    let session_id_start = session_id_len_pos + 1;
-    if handshake.len() < session_id_start + session_id_len {
-        return None;
-    }
-
-    let mut session_id = [0u8; 32];
-    session_id[..session_id_len]
-        .copy_from_slice(&handshake[session_id_start..session_id_start + session_id_len]);
-
-    let now = if !ignore_time_skew {
-        let d = std::time::SystemTime::now()
-            .duration_since(std::time::UNIX_EPOCH)
-            .ok()?;
-        i64::try_from(d.as_secs()).ok()?
-    } else {
-        0_i64
-    };
-
-    let replay_window_u32 = u32::try_from(replay_window_secs).unwrap_or(u32::MAX);
-    let boot_time_cap_secs = if ignore_time_skew {
-        0
-    } else {
-        tls::BOOT_TIME_MAX_SECS
-            .min(replay_window_u32)
-            .min(tls::BOOT_TIME_COMPAT_MAX_SECS)
-    };
-
-    Some(ParsedTlsAuthMaterial {
-        digest,
-        session_id,
-        session_id_len,
-        now,
-        ignore_time_skew,
-        boot_time_cap_secs,
-    })
-}
-
-fn compute_tls_hmac_zeroed_digest(secret: &[u8], handshake: &[u8]) -> [u8; 32] {
-    let mut mac = HmacSha256::new_from_slice(secret).expect("HMAC accepts any key length");
-    mac.update(&handshake[..tls::TLS_DIGEST_POS]);
-    mac.update(&[0u8; tls::TLS_DIGEST_LEN]);
-    mac.update(&handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN..]);
-    mac.finalize().into_bytes().into()
-}
-
-fn validate_tls_secret_candidate(
-    parsed: &ParsedTlsAuthMaterial,
-    handshake: &[u8],
-    secret: &[u8],
-) -> Option<TlsCandidateValidation> {
-    let computed = compute_tls_hmac_zeroed_digest(secret, handshake);
-    if !bool::from(parsed.digest[..28].ct_eq(&computed[..28])) {
-        return None;
-    }
-
-    let timestamp = u32::from_le_bytes([
-        parsed.digest[28] ^ computed[28],
-        parsed.digest[29] ^ computed[29],
-        parsed.digest[30] ^ computed[30],
-        parsed.digest[31] ^ computed[31],
-    ]);
-
-    if !parsed.ignore_time_skew {
-        let is_boot_time = parsed.boot_time_cap_secs > 0 && timestamp < parsed.boot_time_cap_secs;
-        if !is_boot_time {
-            let time_diff = parsed.now - i64::from(timestamp);
-            if !(tls::TIME_SKEW_MIN..=tls::TIME_SKEW_MAX).contains(&time_diff) {
-                return None;
-            }
-        }
-    }
-
-    Some(TlsCandidateValidation {
-        digest: parsed.digest,
-        session_id: parsed.session_id,
-        session_id_len: parsed.session_id_len,
-    })
-}
-
 fn validate_mtproto_secret_candidate(
     handshake: &[u8; HANDSHAKE_LEN],
     dec_prekey: &[u8; PREKEY_LEN],
@@ -1473,14 +1357,60 @@ where
         return HandshakeResult::BadClient { reader, writer };
     }
 
-    let cached = if config.censorship.tls_emulation {
+    let cached_entry = if config.censorship.tls_emulation {
         if let Some(cache) = tls_cache.as_ref() {
             let selected_domain =
                 matched_tls_domain.unwrap_or(config.censorship.tls_domain.as_str());
             let cached_entry = cache.get(selected_domain).await;
-            let use_full_cert_payload = if config.censorship.serverhello_compact
-                && matches!(client_tls_version, tls::ClientHelloTlsVersion::Tls12)
-            {
+            Some(cached_entry)
+        } else {
+            None
+        }
+    } else {
+        None
+    };
+
+    let preferred_key_share_group = cached_entry
+        .as_ref()
+        .and_then(|cached_entry| emulator::profiled_server_hello_key_share_group(cached_entry));
+    let Some(server_key_share) =
+        tls::build_server_hello_key_share(handshake, preferred_key_share_group, rng)
+    else {
+        auth_probe_record_failure_in(shared, peer.ip(), Instant::now());
+        maybe_apply_server_hello_delay(config).await;
+        debug!(
+            peer = %peer,
+            "TLS handshake rejected: ClientHello did not offer a usable TLS 1.3 key_share"
+        );
+        return HandshakeResult::BadClient { reader, writer };
+    };
+
+    let preferred_cipher_suite = if let Some(cached_entry) = cached_entry.as_ref() {
+        if cached_entry.server_hello_template.cipher_suite == [0, 0] {
+            [0x13, 0x01]
+        } else {
+            cached_entry.server_hello_template.cipher_suite
+        }
+    } else {
+        [0x13, 0x01]
+    };
+    let Some(selected_cipher_suite) =
+        tls::select_server_hello_cipher_suite(handshake, preferred_cipher_suite)
+    else {
+        auth_probe_record_failure_in(shared, peer.ip(), Instant::now());
+        maybe_apply_server_hello_delay(config).await;
+        debug!(
+            peer = %peer,
+            "TLS handshake rejected: ClientHello did not offer a supported TLS 1.3 cipher suite"
+        );
+        return HandshakeResult::BadClient { reader, writer };
+    };
+
+    let cached = if let Some(cached_entry) = cached_entry {
+        let use_full_cert_payload = if config.censorship.serverhello_compact
+            && matches!(client_tls_version, tls::ClientHelloTlsVersion::Tls12)
+        {
+            if let Some(cache) = tls_cache.as_ref() {
                 cache
                     .take_full_cert_budget_for_ip(
                         peer.ip(),
@@ -1489,11 +1419,11 @@ where
                     .await
             } else {
                 true
-            };
-            Some((cached_entry, use_full_cert_payload))
+            }
         } else {
-            None
-        }
+            true
+        };
+        Some((cached_entry, use_full_cert_payload))
     } else {
         None
     };
@@ -1512,17 +1442,21 @@ where
             use_full_cert_payload,
             config.censorship.serverhello_compact,
             client_tls_version,
+            selected_cipher_suite,
+            &server_key_share,
             rng,
             selected_alpn.clone(),
             config.censorship.tls_new_session_tickets,
         )
     } else {
-        tls::build_server_hello(
+        tls::build_server_hello_with_cipher(
             &validated_secret,
             &validation_digest,
             validation_session_id_slice,
             config.censorship.fake_cert_len,
             rng,
+            selected_cipher_suite,
+            &server_key_share,
             selected_alpn.clone(),
             config.censorship.tls_new_session_tickets,
         )
@@ -1807,7 +1741,16 @@ where
             return HandshakeResult::BadClient { reader, writer };
         }
 
-        let validation = matched_validation.expect("validation must exist when matched");
+        let Some(validation) = matched_validation else {
+            auth_probe_record_failure_in(shared, peer.ip(), Instant::now());
+            maybe_apply_server_hello_delay(config).await;
+            warn!(
+                peer = %peer,
+                user = %matched_user,
+                "MTProto handshake matched user without validation material"
+            );
+            return HandshakeResult::BadClient { reader, writer };
+        };
 
         if config
             .access

src/proxy/handshake/tls_auth.rs

@@ -0,0 +1,126 @@
+use hmac::{Hmac, Mac};
+use sha2::Sha256;
+use subtle::ConstantTimeEq;
+
+use crate::protocol::tls;
+
+type HmacSha256 = Hmac<Sha256>;
+
+/// Parsed TLS authentication material extracted from a ClientHello candidate.
+#[derive(Clone, Copy)]
+pub(super) struct ParsedTlsAuthMaterial {
+    digest: [u8; tls::TLS_DIGEST_LEN],
+    session_id: [u8; 32],
+    session_id_len: usize,
+    now: i64,
+    ignore_time_skew: bool,
+    boot_time_cap_secs: u32,
+}
+
+/// Successful TLS secret validation output used by the handshake state machine.
+#[derive(Clone, Copy)]
+pub(super) struct TlsCandidateValidation {
+    pub(super) digest: [u8; tls::TLS_DIGEST_LEN],
+    pub(super) session_id: [u8; 32],
+    pub(super) session_id_len: usize,
+}
+
+/// Parse TLS auth digest and session-id material from a candidate handshake.
+pub(super) fn parse_tls_auth_material(
+    handshake: &[u8],
+    ignore_time_skew: bool,
+    replay_window_secs: u64,
+) -> Option<ParsedTlsAuthMaterial> {
+    if handshake.len() < tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN + 1 {
+        return None;
+    }
+
+    let digest: [u8; tls::TLS_DIGEST_LEN] = handshake
+        [tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN]
+        .try_into()
+        .ok()?;
+
+    let session_id_len_pos = tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN;
+    let session_id_len = usize::from(handshake.get(session_id_len_pos).copied()?);
+    if session_id_len > 32 {
+        return None;
+    }
+    let session_id_start = session_id_len_pos + 1;
+    if handshake.len() < session_id_start + session_id_len {
+        return None;
+    }
+
+    let mut session_id = [0u8; 32];
+    session_id[..session_id_len]
+        .copy_from_slice(&handshake[session_id_start..session_id_start + session_id_len]);
+
+    let now = if !ignore_time_skew {
+        let d = std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .ok()?;
+        i64::try_from(d.as_secs()).ok()?
+    } else {
+        0_i64
+    };
+
+    let replay_window_u32 = u32::try_from(replay_window_secs).unwrap_or(u32::MAX);
+    let boot_time_cap_secs = if ignore_time_skew {
+        0
+    } else {
+        tls::BOOT_TIME_MAX_SECS
+            .min(replay_window_u32)
+            .min(tls::BOOT_TIME_COMPAT_MAX_SECS)
+    };
+
+    Some(ParsedTlsAuthMaterial {
+        digest,
+        session_id,
+        session_id_len,
+        now,
+        ignore_time_skew,
+        boot_time_cap_secs,
+    })
+}
+
+fn compute_tls_hmac_zeroed_digest(secret: &[u8], handshake: &[u8]) -> Option<[u8; 32]> {
+    let mut mac = HmacSha256::new_from_slice(secret).ok()?;
+    mac.update(&handshake[..tls::TLS_DIGEST_POS]);
+    mac.update(&[0u8; tls::TLS_DIGEST_LEN]);
+    mac.update(&handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN..]);
+    Some(mac.finalize().into_bytes().into())
+}
+
+/// Validate a candidate secret against parsed TLS authentication material.
+pub(super) fn validate_tls_secret_candidate(
+    parsed: &ParsedTlsAuthMaterial,
+    handshake: &[u8],
+    secret: &[u8],
+) -> Option<TlsCandidateValidation> {
+    let computed = compute_tls_hmac_zeroed_digest(secret, handshake)?;
+    if !bool::from(parsed.digest[..28].ct_eq(&computed[..28])) {
+        return None;
+    }
+
+    let timestamp = u32::from_le_bytes([
+        parsed.digest[28] ^ computed[28],
+        parsed.digest[29] ^ computed[29],
+        parsed.digest[30] ^ computed[30],
+        parsed.digest[31] ^ computed[31],
+    ]);
+
+    if !parsed.ignore_time_skew {
+        let is_boot_time = parsed.boot_time_cap_secs > 0 && timestamp < parsed.boot_time_cap_secs;
+        if !is_boot_time {
+            let time_diff = parsed.now - i64::from(timestamp);
+            if !(tls::TIME_SKEW_MIN..=tls::TIME_SKEW_MAX).contains(&time_diff) {
+                return None;
+            }
+        }
+    }
+
+    Some(TlsCandidateValidation {
+        digest: parsed.digest,
+        session_id: parsed.session_id,
+        session_id_len: parsed.session_id_len,
+    })
+}

src/proxy/masking.rs

@@ -3,12 +3,15 @@
 use crate::config::ProxyConfig;
 use crate::network::dns_overrides::resolve_socket_addr;
 use crate::protocol::tls;
+use crate::proxy::shared_state::ProxySharedState;
 use crate::stats::beobachten::BeobachtenStore;
 use crate::transport::proxy_protocol::{ProxyProtocolV1Builder, ProxyProtocolV2Builder};
+use crate::transport::socket::configure_tcp_socket;
 #[cfg(unix)]
 use nix::ifaddrs::getifaddrs;
 use rand::rngs::StdRng;
 use rand::{Rng, RngExt, SeedableRng};
+use std::io::{Error as IoError, ErrorKind};
 use std::net::{IpAddr, SocketAddr};
 use std::str;
 #[cfg(test)]
@@ -17,7 +20,7 @@ use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::{Mutex, OnceLock};
 use std::time::{Duration, Instant as StdInstant};
 use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
-use tokio::net::TcpStream;
+use tokio::net::{TcpStream, lookup_host};
 #[cfg(unix)]
 use tokio::net::UnixStream;
 #[cfg(unix)]
@@ -36,6 +39,8 @@ const MASK_RELAY_TIMEOUT: Duration = Duration::from_millis(200);
 #[cfg(test)]
 const MASK_RELAY_IDLE_TIMEOUT: Duration = Duration::from_millis(100);
 const MASK_BUFFER_SIZE: usize = 8192;
+const MASK_BUFFER_GROW_AFTER_BYTES: usize = 256 * 1024;
+const MASK_BUFFER_MAX_SIZE: usize = 64 * 1024;
 #[cfg(unix)]
 #[cfg(not(test))]
 const LOCAL_INTERFACE_CACHE_TTL: Duration = Duration::from_secs(300);
@@ -53,6 +58,27 @@ struct MaskTcpTarget<'a> {
     port: u16,
 }
 
+fn mask_copy_read_len(total: usize, byte_cap: usize) -> usize {
+    // Keep short scanner probes on the small baseline buffer and grow only
+    // after the session has proven to be sustained masking relay traffic.
+    let active_buffer_size = if total >= MASK_BUFFER_GROW_AFTER_BYTES {
+        MASK_BUFFER_MAX_SIZE
+    } else {
+        MASK_BUFFER_SIZE
+    };
+
+    if byte_cap == 0 {
+        return active_buffer_size;
+    }
+
+    let remaining_budget = byte_cap.saturating_sub(total);
+    if remaining_budget == 0 {
+        return 0;
+    }
+
+    remaining_budget.min(active_buffer_size)
+}
+
 async fn copy_with_idle_timeout<R, W>(
     reader: &mut R,
     writer: &mut W,
@@ -64,21 +90,18 @@ where
     R: AsyncRead + Unpin,
     W: AsyncWrite + Unpin,
 {
-    let mut buf = Box::new([0u8; MASK_BUFFER_SIZE]);
+    let mut buf = vec![0u8; MASK_BUFFER_SIZE];
     let mut total = 0usize;
     let mut ended_by_eof = false;
-    let unlimited = byte_cap == 0;
 
     loop {
-        let read_len = if unlimited {
-            MASK_BUFFER_SIZE
-        } else {
-            let remaining_budget = byte_cap.saturating_sub(total);
-            if remaining_budget == 0 {
-                break;
-            }
-            remaining_budget.min(MASK_BUFFER_SIZE)
-        };
+        let read_len = mask_copy_read_len(total, byte_cap);
+        if read_len == 0 {
+            break;
+        }
+        if buf.len() < read_len {
+            buf.resize(read_len, 0);
+        }
         let read_res = timeout(idle_timeout, reader.read(&mut buf[..read_len])).await;
         let n = match read_res {
             Ok(Ok(n)) => n,
@@ -250,6 +273,32 @@ async fn consume_client_data_with_timeout_and_cap<R>(
     }
 }
 
+fn mask_failure_drain_cap(config: &ProxyConfig) -> usize {
+    let configured_cap = config.censorship.mask_relay_max_bytes;
+    if configured_cap == 0 {
+        return MASK_BUFFER_SIZE;
+    }
+
+    configured_cap.min(MASK_BUFFER_SIZE)
+}
+
+async fn consume_mask_failure_path<R>(
+    reader: R,
+    config: &ProxyConfig,
+    relay_timeout: Duration,
+    idle_timeout: Duration,
+) where
+    R: AsyncRead + Unpin,
+{
+    consume_client_data_with_timeout_and_cap(
+        reader,
+        mask_failure_drain_cap(config),
+        relay_timeout,
+        idle_timeout,
+    )
+    .await;
+}
+
 async fn wait_mask_connect_budget(started: Instant) {
     let elapsed = started.elapsed();
     if elapsed < MASK_TIMEOUT {
@@ -385,7 +434,7 @@ mod tls_domain_mask_host_tests {
         let mut config = ProxyConfig::default();
         config.censorship.tls_domain = "a.com".to_string();
         config.censorship.tls_domains = vec!["b.com".to_string(), "c.com".to_string()];
-        config.censorship.mask_host = Some("a.com".to_string());
+        config.censorship.mask_host = None;
         config
     }
 
@@ -419,6 +468,15 @@ mod tls_domain_mask_host_tests {
         assert_eq!(mask_host_for_initial_data(&config, &initial_data), "b.com");
     }
 
+    #[test]
+    fn mask_host_uses_primary_domain_when_dynamic_masking_is_disabled() {
+        let mut config = config_with_tls_domains();
+        config.censorship.mask_dynamic = false;
+        let initial_data = client_hello_with_sni("b.com");
+
+        assert_eq!(mask_host_for_initial_data(&config, &initial_data), "a.com");
+    }
+
     #[test]
     fn exclusive_mask_target_overrides_only_matching_sni() {
         let mut config = config_with_tls_domains();
@@ -471,6 +529,32 @@ fn parse_mask_host_ip_literal(host: &str) -> Option<IpAddr> {
     host.parse::<IpAddr>().ok()
 }
 
+async fn resolve_mask_target_addrs(
+    mask_host: &str,
+    mask_port: u16,
+) -> std::io::Result<Vec<SocketAddr>> {
+    if let Some(addr) = resolve_socket_addr(mask_host, mask_port) {
+        return Ok(vec![addr]);
+    }
+
+    if let Some(ip) = parse_mask_host_ip_literal(mask_host) {
+        return Ok(vec![SocketAddr::new(ip, mask_port)]);
+    }
+
+    let addrs = timeout(MASK_TIMEOUT, lookup_host((mask_host, mask_port)))
+        .await
+        .map_err(|_| IoError::new(ErrorKind::TimedOut, "mask target DNS lookup timed out"))??;
+    let addrs = addrs.collect::<Vec<_>>();
+    if addrs.is_empty() {
+        return Err(IoError::new(
+            ErrorKind::NotFound,
+            "mask target DNS lookup returned no addresses",
+        ));
+    }
+
+    Ok(addrs)
+}
+
 fn matching_tls_domain_for_sni<'a>(config: &'a ProxyConfig, sni: &str) -> Option<&'a str> {
     if config.censorship.tls_domain.eq_ignore_ascii_case(sni) {
         return Some(config.censorship.tls_domain.as_str());
@@ -577,24 +661,32 @@ fn default_mask_tcp_target_for_initial_data<'a>(
         .as_deref()
         .unwrap_or(&config.censorship.tls_domain);
 
-    if !configured_mask_host.eq_ignore_ascii_case(&config.censorship.tls_domain) {
+    if config.censorship.mask_host.is_none() && config.censorship.mask_dynamic {
+        let extracted_sni = if sni.is_none() {
+            tls::extract_sni_from_client_hello(initial_data)
+        } else {
+            None
+        };
+        if let Some(host) = sni
+            .or(extracted_sni.as_deref())
+            .and_then(|sni| matching_tls_domain_for_sni(config, sni))
+        {
+            return MaskTcpTarget {
+                host,
+                port: config.censorship.mask_port,
+            };
+        }
+    }
+
+    if let Some(mask_host) = config.censorship.mask_host.as_deref() {
         return MaskTcpTarget {
-            host: configured_mask_host,
+            host: mask_host,
             port: config.censorship.mask_port,
         };
     }
 
-    let extracted_sni = if sni.is_none() {
-        tls::extract_sni_from_client_hello(initial_data)
-    } else {
-        None
-    };
-    let host = sni
-        .or(extracted_sni.as_deref())
-        .and_then(|sni| matching_tls_domain_for_sni(config, sni))
-        .unwrap_or(configured_mask_host);
     MaskTcpTarget {
-        host,
+        host: configured_mask_host,
         port: config.censorship.mask_port,
     }
 }
@@ -744,7 +836,7 @@ fn is_mask_target_local_listener_with_interfaces(
     mask_host: &str,
     mask_port: u16,
     local_addr: SocketAddr,
-    resolved_override: Option<SocketAddr>,
+    resolved_addrs: &[SocketAddr],
     interface_ips: &[IpAddr],
 ) -> bool {
     if mask_port != local_addr.port() {
@@ -754,7 +846,7 @@ fn is_mask_target_local_listener_with_interfaces(
     let local_ip = canonical_ip(local_addr.ip());
     let literal_mask_ip = parse_mask_host_ip_literal(mask_host).map(canonical_ip);
 
-    if let Some(addr) = resolved_override {
+    for addr in resolved_addrs {
         let resolved_ip = canonical_ip(addr.ip());
         if resolved_ip == local_ip {
             return true;
@@ -791,7 +883,7 @@ fn is_mask_target_local_listener(
     mask_host: &str,
     mask_port: u16,
     local_addr: SocketAddr,
-    resolved_override: Option<SocketAddr>,
+    resolved_addrs: &[SocketAddr],
 ) -> bool {
     if mask_port != local_addr.port() {
         return false;
@@ -802,7 +894,7 @@ fn is_mask_target_local_listener(
         mask_host,
         mask_port,
         local_addr,
-        resolved_override,
+        resolved_addrs,
         &interfaces,
     )
 }
@@ -811,7 +903,7 @@ async fn is_mask_target_local_listener_async(
     mask_host: &str,
     mask_port: u16,
     local_addr: SocketAddr,
-    resolved_override: Option<SocketAddr>,
+    resolved_addrs: &[SocketAddr],
 ) -> bool {
     if mask_port != local_addr.port() {
         return false;
@@ -822,7 +914,7 @@ async fn is_mask_target_local_listener_async(
         mask_host,
         mask_port,
         local_addr,
-        resolved_override,
+        resolved_addrs,
         &interfaces,
     )
 }
@@ -860,7 +952,13 @@ fn build_mask_proxy_header(
     }
 }
 
-/// Handle a bad client by forwarding to mask host
+fn configure_mask_backend_socket(stream: &TcpStream) {
+    if let Err(e) = configure_tcp_socket(stream, false, Duration::from_secs(0)) {
+        debug!(error = %e, "Failed to configure mask backend socket");
+    }
+}
+
+/// Handles a bad client by forwarding it to the configured mask target.
 pub async fn handle_bad_client<R, W>(
     reader: R,
     writer: W,
@@ -872,6 +970,34 @@ pub async fn handle_bad_client<R, W>(
 ) where
     R: AsyncRead + Unpin + Send + 'static,
     W: AsyncWrite + Unpin + Send + 'static,
+{
+    let shared = ProxySharedState::new();
+    handle_bad_client_with_shared(
+        reader,
+        writer,
+        initial_data,
+        peer,
+        local_addr,
+        config,
+        beobachten,
+        shared.as_ref(),
+    )
+    .await;
+}
+
+/// Handles a bad client with shared pre-auth fallback admission state.
+pub(crate) async fn handle_bad_client_with_shared<R, W>(
+    reader: R,
+    writer: W,
+    initial_data: &[u8],
+    peer: SocketAddr,
+    local_addr: SocketAddr,
+    config: &ProxyConfig,
+    beobachten: &BeobachtenStore,
+    shared: &ProxySharedState,
+) where
+    R: AsyncRead + Unpin + Send + 'static,
+    W: AsyncWrite + Unpin + Send + 'static,
 {
     let client_type = detect_client_type(initial_data);
     if config.general.beobachten {
@@ -894,6 +1020,17 @@ pub async fn handle_bad_client<R, W>(
         return;
     }
 
+    let Some(_masking_permit) = shared.try_acquire_masking_fallback_permit() else {
+        let outcome_started = Instant::now();
+        debug!(
+            client_type = client_type,
+            "Masking fallback concurrency limit reached"
+        );
+        consume_mask_failure_path(reader, config, relay_timeout, idle_timeout).await;
+        wait_mask_outcome_budget(outcome_started, config).await;
+        return;
+    };
+
     let client_sni = tls::extract_sni_from_client_hello(initial_data);
     let exclusive_tcp_target = client_sni
         .as_deref()
@@ -956,24 +1093,12 @@ pub async fn handle_bad_client<R, W>(
             Ok(Err(e)) => {
                 wait_mask_connect_budget_if_needed(connect_started, config).await;
                 debug!(error = %e, "Failed to connect to mask unix socket");
-                consume_client_data_with_timeout_and_cap(
-                    reader,
-                    config.censorship.mask_relay_max_bytes,
-                    relay_timeout,
-                    idle_timeout,
-                )
-                .await;
+                consume_mask_failure_path(reader, config, relay_timeout, idle_timeout).await;
                 wait_mask_outcome_budget(outcome_started, config).await;
             }
             Err(_) => {
                 debug!("Timeout connecting to mask unix socket");
-                consume_client_data_with_timeout_and_cap(
-                    reader,
-                    config.censorship.mask_relay_max_bytes,
-                    relay_timeout,
-                    idle_timeout,
-                )
-                .await;
+                consume_mask_failure_path(reader, config, relay_timeout, idle_timeout).await;
                 wait_mask_outcome_budget(outcome_started, config).await;
             }
         }
@@ -986,11 +1111,27 @@ pub async fn handle_bad_client<R, W>(
     let mask_host = mask_target.host;
     let mask_port = mask_target.port;
 
+    let resolved_mask_addrs = match resolve_mask_target_addrs(mask_host, mask_port).await {
+        Ok(addrs) => addrs,
+        Err(e) => {
+            let outcome_started = Instant::now();
+            debug!(
+                client_type = client_type,
+                host = %mask_host,
+                port = mask_port,
+                error = %e,
+                "Failed to resolve mask target"
+            );
+            consume_mask_failure_path(reader, config, relay_timeout, idle_timeout).await;
+            wait_mask_outcome_budget(outcome_started, config).await;
+            return;
+        }
+    };
+
     // Fail closed when fallback points at our own listener endpoint.
     // Self-referential masking can create recursive proxy loops under
     // misconfiguration and leak distinguishable load spikes to adversaries.
-    let resolved_mask_addr = resolve_socket_addr(mask_host, mask_port);
-    if is_mask_target_local_listener_async(mask_host, mask_port, local_addr, resolved_mask_addr)
+    if is_mask_target_local_listener_async(mask_host, mask_port, local_addr, &resolved_mask_addrs)
         .await
     {
         let outcome_started = Instant::now();
@@ -1001,13 +1142,7 @@ pub async fn handle_bad_client<R, W>(
             local = %local_addr,
             "Mask target resolves to local listener; refusing self-referential masking fallback"
         );
-        consume_client_data_with_timeout_and_cap(
-            reader,
-            config.censorship.mask_relay_max_bytes,
-            relay_timeout,
-            idle_timeout,
-        )
-        .await;
+        consume_mask_failure_path(reader, config, relay_timeout, idle_timeout).await;
         wait_mask_outcome_budget(outcome_started, config).await;
         return;
     }
@@ -1022,14 +1157,15 @@ pub async fn handle_bad_client<R, W>(
         "Forwarding bad client to mask host"
     );
 
-    // Apply runtime DNS override for mask target when configured.
-    let mask_addr = resolved_mask_addr
-        .map(|addr| addr.to_string())
-        .unwrap_or_else(|| format!("{}:{}", mask_host, mask_port));
     let connect_started = Instant::now();
-    let connect_result = timeout(MASK_TIMEOUT, TcpStream::connect(&mask_addr)).await;
+    let connect_result = timeout(
+        MASK_TIMEOUT,
+        TcpStream::connect(resolved_mask_addrs.as_slice()),
+    )
+    .await;
     match connect_result {
         Ok(Ok(stream)) => {
+            configure_mask_backend_socket(&stream);
             let proxy_header =
                 build_mask_proxy_header(config.censorship.mask_proxy_protocol, peer, local_addr);
 
@@ -1068,24 +1204,12 @@ pub async fn handle_bad_client<R, W>(
         Ok(Err(e)) => {
             wait_mask_connect_budget_if_needed(connect_started, config).await;
             debug!(error = %e, "Failed to connect to mask host");
-            consume_client_data_with_timeout_and_cap(
-                reader,
-                config.censorship.mask_relay_max_bytes,
-                relay_timeout,
-                idle_timeout,
-            )
-            .await;
+            consume_mask_failure_path(reader, config, relay_timeout, idle_timeout).await;
             wait_mask_outcome_budget(outcome_started, config).await;
         }
         Err(_) => {
             debug!("Timeout connecting to mask host");
-            consume_client_data_with_timeout_and_cap(
-                reader,
-                config.censorship.mask_relay_max_bytes,
-                relay_timeout,
-                idle_timeout,
-            )
-            .await;
+            consume_mask_failure_path(reader, config, relay_timeout, idle_timeout).await;
             wait_mask_outcome_budget(outcome_started, config).await;
         }
     }
@@ -1173,20 +1297,17 @@ async fn consume_client_data<R: AsyncRead + Unpin>(
     idle_timeout: Duration,
 ) {
     // Keep drain path fail-closed under slow-loris stalls.
-    let mut buf = Box::new([0u8; MASK_BUFFER_SIZE]);
+    let mut buf = vec![0u8; MASK_BUFFER_SIZE];
     let mut total = 0usize;
-    let unlimited = byte_cap == 0;
 
     loop {
-        let read_len = if unlimited {
-            MASK_BUFFER_SIZE
-        } else {
-            let remaining_budget = byte_cap.saturating_sub(total);
-            if remaining_budget == 0 {
-                break;
-            }
-            remaining_budget.min(MASK_BUFFER_SIZE)
-        };
+        let read_len = mask_copy_read_len(total, byte_cap);
+        if read_len == 0 {
+            break;
+        }
+        if buf.len() < read_len {
+            buf.resize(read_len, 0);
+        }
         let n = match timeout(idle_timeout, reader.read(&mut buf[..read_len])).await {
             Ok(Ok(n)) => n,
             Ok(Err(_)) | Err(_) => break,
@@ -1197,7 +1318,7 @@ async fn consume_client_data<R: AsyncRead + Unpin>(
         }
 
         total = total.saturating_add(n);
-        if !unlimited && total >= byte_cap {
+        if byte_cap != 0 && total >= byte_cap {
             break;
         }
     }
@@ -1315,6 +1436,10 @@ mod masking_interface_cache_concurrency_security_tests;
 #[path = "tests/masking_production_cap_regression_security_tests.rs"]
 mod masking_production_cap_regression_security_tests;
 
+#[cfg(test)]
+#[path = "tests/masking_relay_manual_perf_tests.rs"]
+mod masking_relay_manual_perf_tests;
+
 #[cfg(test)]
 #[path = "tests/masking_extended_attack_surface_security_tests.rs"]
 mod masking_extended_attack_surface_security_tests;

src/proxy/middle_relay.rs

@@ -1,6 +1,6 @@
+use std::collections::BTreeSet;
 #[cfg(test)]
 use std::collections::hash_map::DefaultHasher;
-use std::collections::{BTreeSet, HashMap};
 #[cfg(test)]
 use std::future::Future;
 #[cfg(test)]
@@ -52,7 +52,8 @@ use self::c2me::{
 };
 use self::d2c::{
     MeD2cFlushPolicy, MeWriterResponseOutcome, classify_me_d2c_flush_reason,
-    flush_client_or_cancel, observe_me_d2c_flush_event,
+    flush_client_or_cancel, me_d2c_flush_reason_requires_client_flush,
+    observe_me_d2c_flush_event,
     process_me_writer_response_with_traffic_lease,
 };
 use self::desync::{RelayForensicsState, hash_ip_in, report_desync_frame_too_large_in};

src/proxy/middle_relay/d2c.rs

@@ -55,6 +55,37 @@ pub(super) fn classify_me_d2c_flush_reason(
     MeD2cFlushReason::QueueDrain
 }
 
+pub(super) fn me_d2c_flush_reason_requires_client_flush(reason: MeD2cFlushReason) -> bool {
+    !matches!(reason, MeD2cFlushReason::QueueDrain)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn queue_drain_is_not_a_physical_flush_trigger() {
+        assert!(!me_d2c_flush_reason_requires_client_flush(
+            MeD2cFlushReason::QueueDrain
+        ));
+        assert!(me_d2c_flush_reason_requires_client_flush(
+            MeD2cFlushReason::AckImmediate
+        ));
+        assert!(me_d2c_flush_reason_requires_client_flush(
+            MeD2cFlushReason::BatchFrames
+        ));
+        assert!(me_d2c_flush_reason_requires_client_flush(
+            MeD2cFlushReason::BatchBytes
+        ));
+        assert!(me_d2c_flush_reason_requires_client_flush(
+            MeD2cFlushReason::MaxDelay
+        ));
+        assert!(me_d2c_flush_reason_requires_client_flush(
+            MeD2cFlushReason::Close
+        ));
+    }
+}
+
 pub(super) fn observe_me_d2c_flush_event(
     stats: &Stats,
     reason: MeD2cFlushReason,
@@ -276,20 +307,17 @@ pub(in crate::proxy::middle_relay) fn compute_intermediate_secure_wire_len(
     let wire_len = data_len
         .checked_add(padding_len)
         .ok_or_else(|| ProxyError::Proxy("Frame length overflow".into()))?;
-    if wire_len > 0x7fff_ffffusize {
-        return Err(ProxyError::Proxy(format!(
-            "Intermediate/Secure frame too large: {wire_len}"
-        )));
-    }
-
+    let len_val =
+        crate::protocol::framing::encode_intermediate_header(wire_len, quickack).ok_or_else(
+            || {
+                ProxyError::Proxy(format!(
+                    "Intermediate/Secure frame too large: {wire_len}"
+                ))
+            },
+        )?;
     let total = 4usize
         .checked_add(wire_len)
         .ok_or_else(|| ProxyError::Proxy("Frame buffer size overflow".into()))?;
-    let mut len_val = u32::try_from(wire_len)
-        .map_err(|_| ProxyError::Proxy("Frame length conversion overflow".into()))?;
-    if quickack {
-        len_val |= 0x8000_0000;
-    }
     Ok((len_val, total))
 }
 

src/proxy/middle_relay/idle.rs

@@ -1,4 +1,5 @@
 use super::*;
+use dashmap::DashMap;
 
 mod read;
 
@@ -10,10 +11,10 @@ pub(crate) use self::read::{
 
 #[derive(Default)]
 pub(crate) struct RelayIdleCandidateRegistry {
-    pub(in crate::proxy::middle_relay) by_conn_id: HashMap<u64, RelayIdleCandidateMeta>,
-    pub(in crate::proxy::middle_relay) ordered: BTreeSet<(u64, u64)>,
-    pressure_event_seq: u64,
-    pressure_consumed_seq: u64,
+    pub(in crate::proxy::middle_relay) by_conn_id: DashMap<u64, RelayIdleCandidateMeta>,
+    pub(in crate::proxy::middle_relay) ordered: parking_lot::Mutex<BTreeSet<(u64, u64)>>,
+    pressure_event_seq: AtomicU64,
+    pressure_consumed_seq: AtomicU64,
 }
 
 /// Queue metadata used to preserve FIFO ordering for idle relay eviction.
@@ -23,25 +24,10 @@ pub(in crate::proxy::middle_relay) struct RelayIdleCandidateMeta {
     pub(in crate::proxy::middle_relay) mark_pressure_seq: u64,
 }
 
-pub(super) fn relay_idle_candidate_registry_lock_in(
-    shared: &ProxySharedState,
-) -> std::sync::MutexGuard<'_, RelayIdleCandidateRegistry> {
-    let registry = &shared.middle_relay.relay_idle_registry;
-    match registry.lock() {
-        Ok(guard) => guard,
-        Err(poisoned) => {
-            let mut guard = poisoned.into_inner();
-            *guard = RelayIdleCandidateRegistry::default();
-            registry.clear_poison();
-            guard
-        }
-    }
-}
-
 pub(super) fn mark_relay_idle_candidate_in(shared: &ProxySharedState, conn_id: u64) -> bool {
-    let mut guard = relay_idle_candidate_registry_lock_in(shared);
+    let registry = &shared.middle_relay.relay_idle_registry;
 
-    if guard.by_conn_id.contains_key(&conn_id) {
+    if registry.by_conn_id.contains_key(&conn_id) {
         return false;
     }
 
@@ -52,24 +38,38 @@ pub(super) fn mark_relay_idle_candidate_in(shared: &ProxySharedState, conn_id: u
         .saturating_add(1);
     let meta = RelayIdleCandidateMeta {
         mark_order_seq,
-        mark_pressure_seq: guard.pressure_event_seq,
+        mark_pressure_seq: registry.pressure_event_seq.load(Ordering::Relaxed),
     };
-    guard.by_conn_id.insert(conn_id, meta);
-    guard.ordered.insert((meta.mark_order_seq, conn_id));
-    true
+    match registry.by_conn_id.entry(conn_id) {
+        dashmap::mapref::entry::Entry::Occupied(_) => false,
+        dashmap::mapref::entry::Entry::Vacant(entry) => {
+            entry.insert(meta);
+            registry
+                .ordered
+                .lock()
+                .insert((meta.mark_order_seq, conn_id));
+            true
+        }
+    }
 }
 
 pub(super) fn clear_relay_idle_candidate_in(shared: &ProxySharedState, conn_id: u64) {
-    let mut guard = relay_idle_candidate_registry_lock_in(shared);
+    let registry = &shared.middle_relay.relay_idle_registry;
 
-    if let Some(meta) = guard.by_conn_id.remove(&conn_id) {
-        guard.ordered.remove(&(meta.mark_order_seq, conn_id));
+    if let Some((_, meta)) = registry.by_conn_id.remove(&conn_id) {
+        registry
+            .ordered
+            .lock()
+            .remove(&(meta.mark_order_seq, conn_id));
     }
 }
 
 pub(super) fn note_relay_pressure_event_in(shared: &ProxySharedState) {
-    let mut guard = relay_idle_candidate_registry_lock_in(shared);
-    guard.pressure_event_seq = guard.pressure_event_seq.wrapping_add(1);
+    shared
+        .middle_relay
+        .relay_idle_registry
+        .pressure_event_seq
+        .fetch_add(1, Ordering::Relaxed);
 }
 
 pub(crate) fn note_global_relay_pressure(shared: &ProxySharedState) {
@@ -77,8 +77,11 @@ pub(crate) fn note_global_relay_pressure(shared: &ProxySharedState) {
 }
 
 pub(super) fn relay_pressure_event_seq_in(shared: &ProxySharedState) -> u64 {
-    let guard = relay_idle_candidate_registry_lock_in(shared);
-    guard.pressure_event_seq
+    shared
+        .middle_relay
+        .relay_idle_registry
+        .pressure_event_seq
+        .load(Ordering::Relaxed)
 }
 
 pub(super) fn maybe_evict_idle_candidate_on_pressure_in(
@@ -87,33 +90,52 @@ pub(super) fn maybe_evict_idle_candidate_on_pressure_in(
     seen_pressure_seq: &mut u64,
     stats: &Stats,
 ) -> bool {
-    let mut guard = relay_idle_candidate_registry_lock_in(shared);
+    let registry = &shared.middle_relay.relay_idle_registry;
 
-    let latest_pressure_seq = guard.pressure_event_seq;
+    let latest_pressure_seq = registry.pressure_event_seq.load(Ordering::Relaxed);
     if latest_pressure_seq == *seen_pressure_seq {
         return false;
     }
     *seen_pressure_seq = latest_pressure_seq;
 
-    if latest_pressure_seq == guard.pressure_consumed_seq {
+    let consumed_pressure_seq = registry.pressure_consumed_seq.load(Ordering::Relaxed);
+    if latest_pressure_seq == consumed_pressure_seq {
         return false;
     }
 
-    if guard.ordered.is_empty() {
-        guard.pressure_consumed_seq = latest_pressure_seq;
-        return false;
-    }
-
-    let oldest = guard
-        .ordered
-        .iter()
-        .next()
-        .map(|(_, candidate_conn_id)| *candidate_conn_id);
+    let oldest = {
+        let mut ordered = registry.ordered.lock();
+        loop {
+            let Some((mark_order_seq, candidate_conn_id)) = ordered.iter().next().copied() else {
+                // Empty queues consume the event so later candidates cannot replay stale pressure.
+                let _ = registry.pressure_consumed_seq.compare_exchange(
+                    consumed_pressure_seq,
+                    latest_pressure_seq,
+                    Ordering::Relaxed,
+                    Ordering::Relaxed,
+                );
+                return false;
+            };
+            let Some(candidate_meta) = registry.by_conn_id.get(&candidate_conn_id) else {
+                ordered.remove(&(mark_order_seq, candidate_conn_id));
+                continue;
+            };
+            if candidate_meta.mark_order_seq != mark_order_seq {
+                ordered.remove(&(mark_order_seq, candidate_conn_id));
+                continue;
+            }
+            break Some(candidate_conn_id);
+        }
+    };
     if oldest != Some(conn_id) {
         return false;
     }
 
-    let Some(candidate_meta) = guard.by_conn_id.get(&conn_id).copied() else {
+    let Some(candidate_meta) = registry
+        .by_conn_id
+        .get(&conn_id)
+        .map(|entry| *entry.value())
+    else {
         return false;
     };
 
@@ -121,10 +143,27 @@ pub(super) fn maybe_evict_idle_candidate_on_pressure_in(
         return false;
     }
 
-    if let Some(meta) = guard.by_conn_id.remove(&conn_id) {
-        guard.ordered.remove(&(meta.mark_order_seq, conn_id));
+    // Claim the global pressure budget before removal; otherwise racing sessions
+    // can observe the next FIFO item and spend the same event more than once.
+    if registry
+        .pressure_consumed_seq
+        .compare_exchange(
+            consumed_pressure_seq,
+            latest_pressure_seq,
+            Ordering::Relaxed,
+            Ordering::Relaxed,
+        )
+        .is_err()
+    {
+        return false;
+    }
+
+    if let Some((_, meta)) = registry.by_conn_id.remove(&conn_id) {
+        registry
+            .ordered
+            .lock()
+            .remove(&(meta.mark_order_seq, conn_id));
     }
-    guard.pressure_consumed_seq = latest_pressure_seq;
     stats.increment_relay_pressure_evict_total();
     true
 }
@@ -220,72 +259,32 @@ pub(crate) fn mark_relay_idle_candidate_for_testing(
     shared: &ProxySharedState,
     conn_id: u64,
 ) -> bool {
-    let registry = &shared.middle_relay.relay_idle_registry;
-    let mut guard = match registry.lock() {
-        Ok(guard) => guard,
-        Err(poisoned) => {
-            let mut guard = poisoned.into_inner();
-            *guard = RelayIdleCandidateRegistry::default();
-            registry.clear_poison();
-            guard
-        }
-    };
-
-    if guard.by_conn_id.contains_key(&conn_id) {
-        return false;
-    }
-
-    let mark_order_seq = shared
-        .middle_relay
-        .relay_idle_mark_seq
-        .fetch_add(1, Ordering::Relaxed);
-    let mark_pressure_seq = guard.pressure_event_seq;
-    let meta = RelayIdleCandidateMeta {
-        mark_order_seq,
-        mark_pressure_seq,
-    };
-    guard.by_conn_id.insert(conn_id, meta);
-    guard.ordered.insert((mark_order_seq, conn_id));
-    true
+    mark_relay_idle_candidate_in(shared, conn_id)
 }
 
 #[cfg(test)]
 pub(crate) fn oldest_relay_idle_candidate_for_testing(shared: &ProxySharedState) -> Option<u64> {
     let registry = &shared.middle_relay.relay_idle_registry;
-    let guard = match registry.lock() {
-        Ok(guard) => guard,
-        Err(poisoned) => {
-            let mut guard = poisoned.into_inner();
-            *guard = RelayIdleCandidateRegistry::default();
-            registry.clear_poison();
-            guard
-        }
-    };
-    guard.ordered.iter().next().map(|(_, conn_id)| *conn_id)
+    registry
+        .ordered
+        .lock()
+        .iter()
+        .next()
+        .map(|(_, conn_id)| *conn_id)
 }
 
 #[cfg(test)]
 pub(crate) fn clear_relay_idle_candidate_for_testing(shared: &ProxySharedState, conn_id: u64) {
-    let registry = &shared.middle_relay.relay_idle_registry;
-    let mut guard = match registry.lock() {
-        Ok(guard) => guard,
-        Err(poisoned) => {
-            let mut guard = poisoned.into_inner();
-            *guard = RelayIdleCandidateRegistry::default();
-            registry.clear_poison();
-            guard
-        }
-    };
-    if let Some(meta) = guard.by_conn_id.remove(&conn_id) {
-        guard.ordered.remove(&(meta.mark_order_seq, conn_id));
-    }
+    clear_relay_idle_candidate_in(shared, conn_id);
 }
 
 #[cfg(test)]
 pub(crate) fn clear_relay_idle_pressure_state_for_testing_in_shared(shared: &ProxySharedState) {
-    if let Ok(mut guard) = shared.middle_relay.relay_idle_registry.lock() {
-        *guard = RelayIdleCandidateRegistry::default();
-    }
+    let registry = &shared.middle_relay.relay_idle_registry;
+    registry.by_conn_id.clear();
+    registry.ordered.lock().clear();
+    registry.pressure_event_seq.store(0, Ordering::Relaxed);
+    registry.pressure_consumed_seq.store(0, Ordering::Relaxed);
     shared
         .middle_relay
         .relay_idle_mark_seq
@@ -327,15 +326,10 @@ pub(crate) fn set_relay_pressure_state_for_testing(
     pressure_consumed_seq: u64,
 ) {
     let registry = &shared.middle_relay.relay_idle_registry;
-    let mut guard = match registry.lock() {
-        Ok(guard) => guard,
-        Err(poisoned) => {
-            let mut guard = poisoned.into_inner();
-            *guard = RelayIdleCandidateRegistry::default();
-            registry.clear_poison();
-            guard
-        }
-    };
-    guard.pressure_event_seq = pressure_event_seq;
-    guard.pressure_consumed_seq = pressure_consumed_seq;
+    registry
+        .pressure_event_seq
+        .store(pressure_event_seq, Ordering::Relaxed);
+    registry
+        .pressure_consumed_seq
+        .store(pressure_consumed_seq, Ordering::Relaxed);
 }

src/proxy/middle_relay/idle/read.rs

@@ -236,10 +236,10 @@ where
                     }
                     Err(e) => return Err(e),
                 }
-                let quickack = (len_buf[3] & 0x80) != 0;
+                let header = crate::protocol::framing::parse_intermediate_header(len_buf);
                 (
-                    (u32::from_le_bytes(len_buf) & 0x7fff_ffff) as usize,
-                    quickack,
+                    header.wire_len,
+                    header.quickack,
                     Some(len_buf),
                 )
             }
@@ -331,7 +331,8 @@ where
         )
         .await?;
 
-        // Secure Intermediate: strip validated trailing padding bytes.
+        // Secure Intermediate strips only non-aligned tail padding; full-word
+        // padding is indistinguishable from payload in VersionD framing.
         if proto_tag == ProtoTag::Secure {
             payload.truncate(secure_payload_len);
         }

src/proxy/middle_relay/quota.rs

@@ -41,11 +41,12 @@ pub(super) async fn reserve_user_quota_with_yield(
             return Err(MiddleQuotaReserveError::DeadlineExceeded);
         }
         tokio::select! {
-            _ = tokio::time::sleep(Duration::from_millis(backoff_ms)) => {}
+            biased;
             _ = cancel.cancelled() => {
                 stats.increment_quota_acquire_cancelled_total();
                 return Err(MiddleQuotaReserveError::Cancelled);
             }
+            _ = tokio::time::sleep(Duration::from_millis(backoff_ms)) => {}
         }
         backoff_rounds = backoff_rounds.saturating_add(1);
         if backoff_rounds >= QUOTA_RESERVE_MAX_BACKOFF_ROUNDS {
@@ -128,11 +129,12 @@ pub(super) async fn wait_for_traffic_budget_or_cancel(
             return Err(ProxyError::TrafficBudgetWaitDeadlineExceeded);
         }
         tokio::select! {
-            _ = tokio::time::sleep(next_refill_delay()) => {}
+            biased;
             _ = cancel.cancelled() => {
                 stats.increment_flow_wait_middle_rate_limit_cancelled_total();
                 return Err(ProxyError::TrafficBudgetWaitCancelled);
             }
+            _ = tokio::time::sleep(next_refill_delay()) => {}
         }
         let wait_ms = wait_started_at
             .elapsed()

src/proxy/middle_relay/session.rs

@@ -13,6 +13,7 @@ pub(crate) async fn handle_via_middle_proxy<R, W>(
     mut route_rx: watch::Receiver<RouteCutoverState>,
     route_snapshot: RouteCutoverState,
     session_id: u64,
+    session_cancel: CancellationToken,
     shared: Arc<ProxySharedState>,
 ) -> Result<()>
 where
@@ -20,6 +21,10 @@ where
     W: AsyncWrite + Unpin + Send + 'static,
 {
     let user = success.user.clone();
+    if session_cancel.is_cancelled() {
+        return Err(ProxyError::UserDisabled { user });
+    }
+
     let quota_limit = config.access.user_data_quota.get(&user).copied();
     let quota_user_stats = quota_limit.map(|_| stats.get_or_create_user_stats_handle(&user));
     let peer = success.peer;
@@ -486,12 +491,18 @@ where
                         d2c_flush_policy.max_bytes,
                         max_delay_fired,
                     );
-                    let flush_started_at = if stats_clone.telemetry_policy().me_level.allows_debug() {
+                    let physical_flush =
+                        me_d2c_flush_reason_requires_client_flush(flush_reason);
+                    let flush_started_at = if physical_flush
+                        && stats_clone.telemetry_policy().me_level.allows_debug()
+                    {
                         Some(Instant::now())
                     } else {
                         None
                     };
-                    flush_client_or_cancel(&mut writer, &flow_cancel_me_writer).await?;
+                    if physical_flush {
+                        flush_client_or_cancel(&mut writer, &flow_cancel_me_writer).await?;
+                    }
                     let flush_duration_us = flush_started_at.map(|started| {
                         started
                             .elapsed()
@@ -590,6 +601,25 @@ where
         }
 
         tokio::select! {
+            _ = session_cancel.cancelled() => {
+                warn!(
+                    user = %user,
+                    conn_id,
+                    "Disabled user middle session cancelled"
+                );
+                let _ = enqueue_c2me_command_in(
+                    shared.as_ref(),
+                    &c2me_tx,
+                    C2MeCommand::Close,
+                    c2me_send_timeout,
+                    stats.as_ref(),
+                )
+                .await;
+                main_result = Err(ProxyError::UserDisabled {
+                    user: user.clone(),
+                });
+                break;
+            }
             changed = route_rx.changed(), if route_watch_open => {
                 if changed.is_err() {
                     route_watch_open = false;

src/proxy/relay.rs

@@ -55,11 +55,13 @@ use crate::error::{ProxyError, Result};
 use crate::proxy::traffic_limiter::TrafficLease;
 use crate::stats::Stats;
 use crate::stream::BufferPool;
+use std::future::pending;
 use std::sync::Arc;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::time::Duration;
 use tokio::io::{AsyncRead, AsyncWrite, AsyncWriteExt, copy_bidirectional_with_sizes};
 use tokio::time::Instant;
+use tokio_util::sync::CancellationToken;
 use tracing::{debug, warn};
 
 // ============= Constants =============
@@ -191,6 +193,84 @@ pub async fn relay_bidirectional_with_activity_timeout_and_lease<CR, CW, SR, SW>
     traffic_lease: Option<Arc<TrafficLease>>,
     activity_timeout: Duration,
 ) -> Result<()>
+where
+    CR: AsyncRead + Unpin + Send + 'static,
+    CW: AsyncWrite + Unpin + Send + 'static,
+    SR: AsyncRead + Unpin + Send + 'static,
+    SW: AsyncWrite + Unpin + Send + 'static,
+{
+    relay_bidirectional_with_activity_timeout_lease_cancel_inner(
+        client_reader,
+        client_writer,
+        server_reader,
+        server_writer,
+        c2s_buf_size,
+        s2c_buf_size,
+        user,
+        stats,
+        quota_limit,
+        _buffer_pool,
+        traffic_lease,
+        activity_timeout,
+        None,
+    )
+    .await
+}
+
+pub async fn relay_bidirectional_with_activity_timeout_lease_and_cancel<CR, CW, SR, SW>(
+    client_reader: CR,
+    client_writer: CW,
+    server_reader: SR,
+    server_writer: SW,
+    c2s_buf_size: usize,
+    s2c_buf_size: usize,
+    user: &str,
+    stats: Arc<Stats>,
+    quota_limit: Option<u64>,
+    _buffer_pool: Arc<BufferPool>,
+    traffic_lease: Option<Arc<TrafficLease>>,
+    activity_timeout: Duration,
+    session_cancel: CancellationToken,
+) -> Result<()>
+where
+    CR: AsyncRead + Unpin + Send + 'static,
+    CW: AsyncWrite + Unpin + Send + 'static,
+    SR: AsyncRead + Unpin + Send + 'static,
+    SW: AsyncWrite + Unpin + Send + 'static,
+{
+    relay_bidirectional_with_activity_timeout_lease_cancel_inner(
+        client_reader,
+        client_writer,
+        server_reader,
+        server_writer,
+        c2s_buf_size,
+        s2c_buf_size,
+        user,
+        stats,
+        quota_limit,
+        _buffer_pool,
+        traffic_lease,
+        activity_timeout,
+        Some(session_cancel),
+    )
+    .await
+}
+
+async fn relay_bidirectional_with_activity_timeout_lease_cancel_inner<CR, CW, SR, SW>(
+    client_reader: CR,
+    client_writer: CW,
+    server_reader: SR,
+    server_writer: SW,
+    c2s_buf_size: usize,
+    s2c_buf_size: usize,
+    user: &str,
+    stats: Arc<Stats>,
+    quota_limit: Option<u64>,
+    _buffer_pool: Arc<BufferPool>,
+    traffic_lease: Option<Arc<TrafficLease>>,
+    activity_timeout: Duration,
+    session_cancel: Option<CancellationToken>,
+) -> Result<()>
 where
     CR: AsyncRead + Unpin + Send + 'static,
     CW: AsyncWrite + Unpin + Send + 'static,
@@ -287,14 +367,29 @@ where
     //
     // When the watchdog fires, select! drops the copy future,
     // releasing the &mut borrows on client and server.
-    let copy_result = tokio::select! {
+    enum RelayOutcome {
+        Copy(std::io::Result<(u64, u64)>),
+        ActivityTimeout,
+        UserDisabled,
+    }
+
+    let cancel_wait = async move {
+        match session_cancel {
+            Some(token) => token.cancelled().await,
+            None => pending::<()>().await,
+        }
+    };
+    tokio::pin!(cancel_wait);
+
+    let relay_outcome = tokio::select! {
         result = copy_bidirectional_with_sizes(
             &mut client,
             &mut server,
             c2s_buf_size.max(1),
             s2c_buf_size.max(1),
-        ) => Some(result),
-        _ = watchdog => None, // Activity timeout — cancel relay
+        ) => RelayOutcome::Copy(result),
+        _ = watchdog => RelayOutcome::ActivityTimeout,
+        _ = &mut cancel_wait => RelayOutcome::UserDisabled,
     };
 
     // ── Clean shutdown ──────────────────────────────────────────────
@@ -308,8 +403,8 @@ where
     let s2c_ops = counters.s2c_ops.load(Ordering::Relaxed);
     let duration = epoch.elapsed();
 
-    match copy_result {
-        Some(Ok((c2s, s2c))) => {
+    match relay_outcome {
+        RelayOutcome::Copy(Ok((c2s, s2c))) => {
             // Normal completion — one side closed the connection
             debug!(
                 user = %user_owned,
@@ -322,7 +417,7 @@ where
             );
             Ok(())
         }
-        Some(Err(e)) if is_quota_io_error(&e) => {
+        RelayOutcome::Copy(Err(e)) if is_quota_io_error(&e) => {
             let c2s = counters.c2s_bytes.load(Ordering::Relaxed);
             let s2c = counters.s2c_bytes.load(Ordering::Relaxed);
             warn!(
@@ -338,7 +433,7 @@ where
                 user: user_owned.clone(),
             })
         }
-        Some(Err(e)) => {
+        RelayOutcome::Copy(Err(e)) => {
             // I/O error in one of the directions
             let c2s = counters.c2s_bytes.load(Ordering::Relaxed);
             let s2c = counters.s2c_bytes.load(Ordering::Relaxed);
@@ -354,7 +449,7 @@ where
             );
             Err(e.into())
         }
-        None => {
+        RelayOutcome::ActivityTimeout => {
             // Activity timeout (watchdog fired)
             let c2s = counters.c2s_bytes.load(Ordering::Relaxed);
             let s2c = counters.s2c_bytes.load(Ordering::Relaxed);
@@ -369,6 +464,22 @@ where
             );
             Ok(())
         }
+        RelayOutcome::UserDisabled => {
+            let c2s = counters.c2s_bytes.load(Ordering::Relaxed);
+            let s2c = counters.s2c_bytes.load(Ordering::Relaxed);
+            debug!(
+                user = %user_owned,
+                c2s_bytes = c2s,
+                s2c_bytes = s2c,
+                c2s_msgs = c2s_ops,
+                s2c_msgs = s2c_ops,
+                duration_secs = duration.as_secs(),
+                "Relay finished (user disabled)"
+            );
+            Err(ProxyError::UserDisabled {
+                user: user_owned.clone(),
+            })
+        }
     }
 }
 

src/proxy/shared_state.rs

@@ -1,18 +1,20 @@
-use std::collections::HashSet;
 use std::collections::hash_map::RandomState;
+use std::collections::{HashMap, HashSet};
 use std::net::{IpAddr, SocketAddr};
 use std::sync::atomic::{AtomicBool, AtomicU32, AtomicU64, Ordering};
 use std::sync::{Arc, Mutex};
 use std::time::Instant;
 
 use dashmap::DashMap;
-use tokio::sync::mpsc;
+use tokio::sync::{OwnedSemaphorePermit, Semaphore, mpsc};
+use tokio_util::sync::CancellationToken;
 
 use crate::proxy::handshake::{AuthProbeSaturationState, AuthProbeState};
 use crate::proxy::middle_relay::{DesyncDedupRotationState, RelayIdleCandidateRegistry};
 use crate::proxy::traffic_limiter::TrafficLimiter;
 
 const HANDSHAKE_RECENT_USER_RING_LEN: usize = 64;
+const MASKING_FALLBACK_MAX_CONCURRENT: usize = 512;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub(crate) enum ConntrackCloseReason {
@@ -59,7 +61,7 @@ pub(crate) struct MiddleRelaySharedState {
     pub(crate) desync_hasher: RandomState,
     pub(crate) desync_full_cache_last_emit_at: Mutex<Option<Instant>>,
     pub(crate) desync_dedup_rotation_state: Mutex<DesyncDedupRotationState>,
-    pub(crate) relay_idle_registry: Mutex<RelayIdleCandidateRegistry>,
+    pub(crate) relay_idle_registry: RelayIdleCandidateRegistry,
     pub(crate) relay_idle_mark_seq: AtomicU64,
 }
 
@@ -67,8 +69,34 @@ pub(crate) struct ProxySharedState {
     pub(crate) handshake: HandshakeSharedState,
     pub(crate) middle_relay: MiddleRelaySharedState,
     pub(crate) traffic_limiter: Arc<TrafficLimiter>,
+    disabled_users: DashMap<String, ()>,
+    active_user_sessions: DashMap<(String, u64), CancellationToken>,
     pub(crate) conntrack_pressure_active: AtomicBool,
     pub(crate) conntrack_close_tx: Mutex<Option<mpsc::Sender<ConntrackCloseEvent>>>,
+    masking_fallback_permits: Arc<Semaphore>,
+}
+
+#[must_use = "registered user sessions must be kept alive until relay completion"]
+pub(crate) struct UserSessionRegistration {
+    token: CancellationToken,
+    _guard: UserSessionGuard,
+}
+
+impl UserSessionRegistration {
+    pub(crate) fn token(&self) -> CancellationToken {
+        self.token.clone()
+    }
+}
+
+struct UserSessionGuard {
+    shared: Arc<ProxySharedState>,
+    key: (String, u64),
+}
+
+impl Drop for UserSessionGuard {
+    fn drop(&mut self) {
+        self.shared.active_user_sessions.remove(&self.key);
+    }
 }
 
 impl ProxySharedState {
@@ -97,15 +125,95 @@ impl ProxySharedState {
                 desync_hasher: RandomState::new(),
                 desync_full_cache_last_emit_at: Mutex::new(None),
                 desync_dedup_rotation_state: Mutex::new(DesyncDedupRotationState::default()),
-                relay_idle_registry: Mutex::new(RelayIdleCandidateRegistry::default()),
+                relay_idle_registry: RelayIdleCandidateRegistry::default(),
                 relay_idle_mark_seq: AtomicU64::new(0),
             },
             traffic_limiter: TrafficLimiter::new(),
+            disabled_users: DashMap::new(),
+            active_user_sessions: DashMap::new(),
             conntrack_pressure_active: AtomicBool::new(false),
             conntrack_close_tx: Mutex::new(None),
+            masking_fallback_permits: Arc::new(Semaphore::new(MASKING_FALLBACK_MAX_CONCURRENT)),
         })
     }
 
+    /// Attempts to reserve one masking fallback slot for a pre-auth connection.
+    pub(crate) fn try_acquire_masking_fallback_permit(&self) -> Option<OwnedSemaphorePermit> {
+        self.masking_fallback_permits
+            .clone()
+            .try_acquire_owned()
+            .ok()
+    }
+
+    pub(crate) fn is_user_enabled(&self, user: &str) -> bool {
+        !self.disabled_users.contains_key(user)
+    }
+
+    pub(crate) fn set_user_enabled(&self, user: &str, enabled: bool) -> bool {
+        if enabled {
+            self.disabled_users.remove(user);
+            false
+        } else {
+            self.disabled_users.insert(user.to_string(), ()).is_none()
+        }
+    }
+
+    pub(crate) fn apply_user_enabled_config(
+        &self,
+        user_enabled: &HashMap<String, bool>,
+    ) -> Vec<String> {
+        let desired_disabled = user_enabled
+            .iter()
+            .filter_map(|(user, enabled)| (!*enabled).then_some(user.clone()))
+            .collect::<HashSet<_>>();
+        let current_disabled = self
+            .disabled_users
+            .iter()
+            .map(|entry| entry.key().clone())
+            .collect::<HashSet<_>>();
+
+        for user in current_disabled.difference(&desired_disabled) {
+            self.disabled_users.remove(user);
+        }
+        let newly_disabled = desired_disabled
+            .difference(&current_disabled)
+            .cloned()
+            .collect::<Vec<_>>();
+        for user in desired_disabled {
+            self.disabled_users.insert(user, ());
+        }
+        newly_disabled
+    }
+
+    pub(crate) fn register_user_session(
+        self: &Arc<Self>,
+        user: &str,
+        session_id: u64,
+    ) -> UserSessionRegistration {
+        let token = CancellationToken::new();
+        let key = (user.to_string(), session_id);
+        self.active_user_sessions.insert(key.clone(), token.clone());
+        UserSessionRegistration {
+            token,
+            _guard: UserSessionGuard {
+                shared: Arc::clone(self),
+                key,
+            },
+        }
+    }
+
+    pub(crate) fn cancel_user_sessions(&self, user: &str) -> usize {
+        let tokens = self
+            .active_user_sessions
+            .iter()
+            .filter_map(|entry| (entry.key().0 == user).then(|| entry.value().clone()))
+            .collect::<Vec<_>>();
+        for token in &tokens {
+            token.cancel();
+        }
+        tokens.len()
+    }
+
     pub(crate) fn set_conntrack_close_sender(&self, tx: mpsc::Sender<ConntrackCloseEvent>) {
         match self.conntrack_close_tx.lock() {
             Ok(mut guard) => {
@@ -166,3 +274,48 @@ impl ProxySharedState {
         self.conntrack_pressure_active.load(Ordering::Relaxed)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn user_enabled_config_sync_tracks_disabled_overrides() {
+        let shared = ProxySharedState::new();
+        assert!(shared.is_user_enabled("alice"));
+
+        let mut user_enabled = HashMap::new();
+        user_enabled.insert("alice".to_string(), false);
+        user_enabled.insert("bob".to_string(), true);
+
+        let mut newly_disabled = shared.apply_user_enabled_config(&user_enabled);
+        newly_disabled.sort();
+        assert_eq!(newly_disabled, vec!["alice".to_string()]);
+        assert!(!shared.is_user_enabled("alice"));
+        assert!(shared.is_user_enabled("bob"));
+
+        assert!(shared.apply_user_enabled_config(&user_enabled).is_empty());
+
+        user_enabled.clear();
+        assert!(shared.apply_user_enabled_config(&user_enabled).is_empty());
+        assert!(shared.is_user_enabled("alice"));
+    }
+
+    #[test]
+    fn cancel_user_sessions_cancels_only_registered_matching_user() {
+        let shared = ProxySharedState::new();
+        let alice_1 = shared.register_user_session("alice", 1);
+        let alice_2 = shared.register_user_session("alice", 2);
+        let bob = shared.register_user_session("bob", 1);
+        let alice_1_token = alice_1.token();
+        let alice_2_token = alice_2.token();
+        let bob_token = bob.token();
+
+        drop(alice_1);
+
+        assert_eq!(shared.cancel_user_sessions("alice"), 1);
+        assert!(!alice_1_token.is_cancelled());
+        assert!(alice_2_token.is_cancelled());
+        assert!(!bob_token.is_cancelled());
+    }
+}

src/proxy/tests/client_masking_blackhat_campaign_tests.rs

@@ -39,6 +39,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -85,17 +86,72 @@ fn make_valid_tls_client_hello(secret: &[u8], timestamp: u32, tls_len: usize, fi
         "TLS length must fit into record header"
     );
 
-    let total_len = 5 + tls_len;
-    let mut handshake = vec![fill; total_len];
-
-    handshake[0] = 0x16;
-    handshake[1] = 0x03;
-    handshake[2] = 0x01;
-    handshake[3..5].copy_from_slice(&(tls_len as u16).to_be_bytes());
-
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const TLS_EXTENSION_PADDING: u16 = 0x0015;
+    const X25519_KEY_SHARE_LEN: usize = 32;
     let session_id_len: usize = 32;
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
 
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let base_tls_len = 4
+        + 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    assert!(
+        tls_len == base_tls_len || tls_len >= base_tls_len + 4,
+        "TLS length must leave room for a complete padding extension"
+    );
+    if tls_len > base_tls_len {
+        let padding_len = tls_len - base_tls_len - 4;
+        extensions.extend_from_slice(&TLS_EXTENSION_PADDING.to_be_bytes());
+        extensions.extend_from_slice(&(padding_len as u16).to_be_bytes());
+        extensions.resize(extensions.len() + padding_len, fill);
+    }
+
+    let body_len = tls_len - 4;
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + tls_len);
+    handshake.push(0x16);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&(tls_len as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
     handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
     let computed = sha256_hmac(secret, &handshake);
     let mut digest = computed;
@@ -182,10 +238,11 @@ async fn run_tls_success_mtproto_fail_capture(
     assert_eq!(tls_response_head[0], 0x16);
     read_and_discard_tls_record_body(&mut client_side, tls_response_head).await;
 
-    client_side.write_all(&bad_mtproto_record).await.unwrap();
+    let mut client_payload = bad_mtproto_record;
     for record in trailing_records {
-        client_side.write_all(&record).await.unwrap();
+        client_payload.extend_from_slice(&record);
     }
+    client_side.write_all(&client_payload).await.unwrap();
 
     let got = tokio::time::timeout(Duration::from_secs(4), accept_task)
         .await
@@ -434,11 +491,9 @@ async fn blackhat_campaign_06_replayed_tls_hello_is_masked_without_serverhello()
                 client_side.read_exact(&mut head).await.unwrap();
                 assert_eq!(head[0], 0x16);
                 read_and_discard_tls_record_body(&mut client_side, head).await;
-                client_side
-                    .write_all(&invalid_mtproto_record)
-                    .await
-                    .unwrap();
-                client_side.write_all(&first_tail).await.unwrap();
+                let mut client_payload = invalid_mtproto_record;
+                client_payload.extend_from_slice(&first_tail);
+                client_side.write_all(&client_payload).await.unwrap();
             } else {
                 let mut one = [0u8; 1];
                 let no_server_hello = tokio::time::timeout(
@@ -740,8 +795,9 @@ async fn blackhat_campaign_12_parallel_tls_success_mtproto_fail_sessions_keep_is
             let mut head = [0u8; 5];
             client_side.read_exact(&mut head).await.unwrap();
             read_and_discard_tls_record_body(&mut client_side, head).await;
-            client_side.write_all(&bad).await.unwrap();
-            client_side.write_all(&tail).await.unwrap();
+            let mut client_payload = bad;
+            client_payload.extend_from_slice(&tail);
+            client_side.write_all(&client_payload).await.unwrap();
             client_side.shutdown().await.unwrap();
 
             let result = tokio::time::timeout(Duration::from_secs(5), handler)

src/proxy/tests/client_masking_budget_security_tests.rs

@@ -35,6 +35,7 @@ fn build_harness(config: ProxyConfig) -> PipelineHarness {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -64,17 +65,72 @@ fn make_valid_tls_client_hello(secret: &[u8], timestamp: u32, tls_len: usize, fi
         "TLS length must fit into record header"
     );
 
-    let total_len = 5 + tls_len;
-    let mut handshake = vec![fill; total_len];
-
-    handshake[0] = 0x16;
-    handshake[1] = 0x03;
-    handshake[2] = 0x01;
-    handshake[3..5].copy_from_slice(&(tls_len as u16).to_be_bytes());
-
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const TLS_EXTENSION_PADDING: u16 = 0x0015;
+    const X25519_KEY_SHARE_LEN: usize = 32;
     let session_id_len: usize = 32;
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
 
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let base_tls_len = 4
+        + 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    assert!(
+        tls_len == base_tls_len || tls_len >= base_tls_len + 4,
+        "TLS length must leave room for a complete padding extension"
+    );
+    if tls_len > base_tls_len {
+        let padding_len = tls_len - base_tls_len - 4;
+        extensions.extend_from_slice(&TLS_EXTENSION_PADDING.to_be_bytes());
+        extensions.extend_from_slice(&(padding_len as u16).to_be_bytes());
+        extensions.resize(extensions.len() + padding_len, fill);
+    }
+
+    let body_len = tls_len - 4;
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + tls_len);
+    handshake.push(0x16);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&(tls_len as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
     handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
     let computed = sha256_hmac(secret, &handshake);
     let mut digest = computed;
@@ -239,11 +295,9 @@ async fn tls_mtproto_bad_client_does_not_reinject_clienthello_into_mask_backend(
     assert_eq!(tls_response_head[0], 0x16);
     read_and_discard_tls_record_body(&mut client_side, tls_response_head).await;
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    client_side.write_all(&trailing_record).await.unwrap();
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&trailing_record);
+    client_side.write_all(&client_payload).await.unwrap();
 
     tokio::time::timeout(Duration::from_secs(3), accept_task)
         .await

src/proxy/tests/client_masking_diagnostics_security_tests.rs

@@ -19,6 +19,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,

src/proxy/tests/client_masking_fragmented_classifier_security_tests.rs

@@ -19,6 +19,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,

src/proxy/tests/client_masking_hard_adversarial_tests.rs

@@ -33,6 +33,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -79,17 +80,72 @@ fn make_valid_tls_client_hello(secret: &[u8], timestamp: u32, tls_len: usize, fi
         "TLS length must fit into record header"
     );
 
-    let total_len = 5 + tls_len;
-    let mut handshake = vec![fill; total_len];
-
-    handshake[0] = 0x16;
-    handshake[1] = 0x03;
-    handshake[2] = 0x01;
-    handshake[3..5].copy_from_slice(&(tls_len as u16).to_be_bytes());
-
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const TLS_EXTENSION_PADDING: u16 = 0x0015;
+    const X25519_KEY_SHARE_LEN: usize = 32;
     let session_id_len: usize = 32;
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
 
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let base_tls_len = 4
+        + 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    assert!(
+        tls_len == base_tls_len || tls_len >= base_tls_len + 4,
+        "TLS length must leave room for a complete padding extension"
+    );
+    if tls_len > base_tls_len {
+        let padding_len = tls_len - base_tls_len - 4;
+        extensions.extend_from_slice(&TLS_EXTENSION_PADDING.to_be_bytes());
+        extensions.extend_from_slice(&(padding_len as u16).to_be_bytes());
+        extensions.resize(extensions.len() + padding_len, fill);
+    }
+
+    let body_len = tls_len - 4;
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + tls_len);
+    handshake.push(0x16);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&(tls_len as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
     handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
     let computed = sha256_hmac(secret, &handshake);
     let mut digest = computed;
@@ -172,13 +228,11 @@ async fn run_tls_success_mtproto_fail_capture(
     assert_eq!(tls_response_head[0], 0x16);
     read_tls_record_body(&mut client_side, tls_response_head).await;
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
+    let mut client_payload = invalid_mtproto_record;
     for record in trailing_records {
-        client_side.write_all(&record).await.unwrap();
+        client_payload.extend_from_slice(&record);
     }
+    client_side.write_all(&client_payload).await.unwrap();
 
     let got = tokio::time::timeout(Duration::from_secs(3), accept_task)
         .await
@@ -343,11 +397,9 @@ async fn replayed_tls_hello_gets_no_serverhello_and_is_masked() {
                 client_side.read_exact(&mut head).await.unwrap();
                 assert_eq!(head[0], 0x16);
                 read_tls_record_body(&mut client_side, head).await;
-                client_side
-                    .write_all(&invalid_mtproto_record)
-                    .await
-                    .unwrap();
-                client_side.write_all(&first_tail).await.unwrap();
+                let mut client_payload = invalid_mtproto_record;
+                client_payload.extend_from_slice(&first_tail);
+                client_side.write_all(&client_payload).await.unwrap();
             } else {
                 let mut one = [0u8; 1];
                 let no_server_hello = tokio::time::timeout(
@@ -418,11 +470,9 @@ async fn connects_bad_increments_once_per_invalid_mtproto() {
     let mut head = [0u8; 5];
     client_side.read_exact(&mut head).await.unwrap();
     read_tls_record_body(&mut client_side, head).await;
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    client_side.write_all(&tail).await.unwrap();
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&tail);
+    client_side.write_all(&client_payload).await.unwrap();
 
     tokio::time::timeout(Duration::from_secs(3), accept_task)
         .await
@@ -675,8 +725,9 @@ async fn concurrent_tls_mtproto_fail_sessions_are_isolated() {
             let mut head = [0u8; 5];
             client_side.read_exact(&mut head).await.unwrap();
             read_tls_record_body(&mut client_side, head).await;
-            client_side.write_all(&invalid_mtproto).await.unwrap();
-            client_side.write_all(&trailing).await.unwrap();
+            let mut client_payload = invalid_mtproto;
+            client_payload.extend_from_slice(&trailing);
+            client_side.write_all(&client_payload).await.unwrap();
             client_side.shutdown().await.unwrap();
 
             let _ = tokio::time::timeout(Duration::from_secs(3), handler)

src/proxy/tests/client_masking_http2_fragmented_preface_security_tests.rs

@@ -19,6 +19,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,

src/proxy/tests/client_masking_prefetch_config_pipeline_integration_security_tests.rs

@@ -19,6 +19,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,

src/proxy/tests/client_masking_prefetch_invariant_security_tests.rs

@@ -46,6 +46,7 @@ fn build_harness(secret_hex: &str, mask_port: u16) -> PipelineHarness {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -70,17 +71,77 @@ fn build_harness(secret_hex: &str, mask_port: u16) -> PipelineHarness {
 }
 
 fn make_valid_tls_client_hello(secret: &[u8], timestamp: u32, tls_len: usize, fill: u8) -> Vec<u8> {
-    let total_len = 5 + tls_len;
-    let mut handshake = vec![fill; total_len];
-
-    handshake[0] = 0x16;
-    handshake[1] = 0x03;
-    handshake[2] = 0x01;
-    handshake[3..5].copy_from_slice(&(tls_len as u16).to_be_bytes());
+    assert!(
+        tls_len <= u16::MAX as usize,
+        "TLS length must fit into record header"
+    );
 
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const TLS_EXTENSION_PADDING: u16 = 0x0015;
+    const X25519_KEY_SHARE_LEN: usize = 32;
     let session_id_len: usize = 32;
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
 
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let base_tls_len = 4
+        + 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    assert!(
+        tls_len == base_tls_len || tls_len >= base_tls_len + 4,
+        "TLS length must leave room for a complete padding extension"
+    );
+    if tls_len > base_tls_len {
+        let padding_len = tls_len - base_tls_len - 4;
+        extensions.extend_from_slice(&TLS_EXTENSION_PADDING.to_be_bytes());
+        extensions.extend_from_slice(&(padding_len as u16).to_be_bytes());
+        extensions.resize(extensions.len() + padding_len, fill);
+    }
+
+    let body_len = tls_len - 4;
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + tls_len);
+    handshake.push(0x16);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&(tls_len as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
     handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
     let computed = sha256_hmac(secret, &handshake);
     let mut digest = computed;
@@ -249,11 +310,9 @@ async fn blackhat_integration_empty_initial_data_path_is_byte_exact_and_eof_clea
     assert_eq!(head[0], 0x16);
     read_and_discard_tls_record_body(&mut client_side, head).await;
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    client_side.write_all(&trailing_record).await.unwrap();
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&trailing_record);
+    client_side.write_all(&client_payload).await.unwrap();
     client_side.shutdown().await.unwrap();
 
     tokio::time::timeout(Duration::from_secs(3), accept_task)

src/proxy/tests/client_masking_probe_evasion_blackhat_tests.rs

@@ -24,6 +24,7 @@ fn make_test_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,

src/proxy/tests/client_masking_redteam_expected_fail_tests.rs

@@ -47,6 +47,7 @@ fn build_harness(secret_hex: &str, mask_port: u16) -> RedTeamHarness {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -76,17 +77,73 @@ fn make_valid_tls_client_hello(secret: &[u8], timestamp: u32, tls_len: usize, fi
         "TLS length must fit into record header"
     );
 
-    let total_len = 5 + tls_len;
-    let mut handshake = vec![fill; total_len];
-    handshake[0] = 0x16;
-    handshake[1] = 0x03;
-    handshake[2] = 0x01;
-    handshake[3..5].copy_from_slice(&(tls_len as u16).to_be_bytes());
-
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const TLS_EXTENSION_PADDING: u16 = 0x0015;
+    const X25519_KEY_SHARE_LEN: usize = 32;
     let session_id_len: usize = 32;
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
-    handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
 
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let base_tls_len = 4
+        + 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    assert!(
+        tls_len == base_tls_len || tls_len >= base_tls_len + 4,
+        "TLS length must leave room for a complete padding extension"
+    );
+    if tls_len > base_tls_len {
+        let padding_len = tls_len - base_tls_len - 4;
+        extensions.extend_from_slice(&TLS_EXTENSION_PADDING.to_be_bytes());
+        extensions.extend_from_slice(&(padding_len as u16).to_be_bytes());
+        extensions.resize(extensions.len() + padding_len, fill);
+    }
+
+    let body_len = tls_len - 4;
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + tls_len);
+    handshake.push(0x16);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&(tls_len as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
+    handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
     let computed = sha256_hmac(secret, &handshake);
     let mut digest = computed;
     let ts = timestamp.to_le_bytes();
@@ -155,14 +212,9 @@ async fn run_tls_success_mtproto_fail_session(
     let mut body = vec![0u8; body_len];
     client_side.read_exact(&mut body).await.unwrap();
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    client_side
-        .write_all(&wrap_tls_application_data(&tail))
-        .await
-        .unwrap();
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&wrap_tls_application_data(&tail));
+    client_side.write_all(&client_payload).await.unwrap();
 
     let forwarded = tokio::time::timeout(Duration::from_secs(3), accept_task)
         .await
@@ -240,6 +292,7 @@ async fn redteam_03_masking_duration_must_be_less_than_1ms_when_backend_down() {
                 selected_scope: String::new(),
                 ipv4: None,
                 ipv6: None,
+                prefer: None,
             }],
             1,
             1,
@@ -484,6 +537,7 @@ async fn measure_invalid_probe_duration_ms(delay_ms: u64, tls_len: u16, body_sen
                 selected_scope: String::new(),
                 ipv4: None,
                 ipv6: None,
+                prefer: None,
             }],
             1,
             1,
@@ -561,6 +615,7 @@ async fn capture_forwarded_probe_len(tls_len: u16, body_sent: usize) -> usize {
                 selected_scope: String::new(),
                 ipv4: None,
                 ipv6: None,
+                prefer: None,
             }],
             1,
             1,

src/proxy/tests/client_masking_replay_timing_security_tests.rs

@@ -21,6 +21,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -33,17 +34,77 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
 }
 
 fn make_valid_tls_client_hello(secret: &[u8], timestamp: u32, tls_len: usize, fill: u8) -> Vec<u8> {
-    let total_len = 5 + tls_len;
-    let mut handshake = vec![fill; total_len];
-
-    handshake[0] = 0x16;
-    handshake[1] = 0x03;
-    handshake[2] = 0x01;
-    handshake[3..5].copy_from_slice(&(tls_len as u16).to_be_bytes());
+    assert!(
+        tls_len <= u16::MAX as usize,
+        "TLS length must fit into record header"
+    );
 
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const TLS_EXTENSION_PADDING: u16 = 0x0015;
+    const X25519_KEY_SHARE_LEN: usize = 32;
     let session_id_len: usize = 32;
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
 
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let base_tls_len = 4
+        + 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    assert!(
+        tls_len == base_tls_len || tls_len >= base_tls_len + 4,
+        "TLS length must leave room for a complete padding extension"
+    );
+    if tls_len > base_tls_len {
+        let padding_len = tls_len - base_tls_len - 4;
+        extensions.extend_from_slice(&TLS_EXTENSION_PADDING.to_be_bytes());
+        extensions.extend_from_slice(&(padding_len as u16).to_be_bytes());
+        extensions.resize(extensions.len() + padding_len, fill);
+    }
+
+    let body_len = tls_len - 4;
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + tls_len);
+    handshake.push(0x16);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&(tls_len as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
     handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
     let computed = sha256_hmac(secret, &handshake);
     let mut digest = computed;
@@ -118,14 +179,9 @@ async fn run_replay_candidate_session(
         invalid_mtproto_record.extend_from_slice(&TLS_VERSION);
         invalid_mtproto_record.extend_from_slice(&(HANDSHAKE_LEN as u16).to_be_bytes());
         invalid_mtproto_record.extend_from_slice(&vec![0u8; HANDSHAKE_LEN]);
-        client_side
-            .write_all(&invalid_mtproto_record)
-            .await
-            .unwrap();
-        client_side
-            .write_all(b"GET /replay-fallback HTTP/1.1\r\nHost: x\r\n\r\n")
-            .await
-            .unwrap();
+        let mut client_payload = invalid_mtproto_record;
+        client_payload.extend_from_slice(b"GET /replay-fallback HTTP/1.1\r\nHost: x\r\n\r\n");
+        client_side.write_all(&client_payload).await.unwrap();
     }
 
     client_side.shutdown().await.unwrap();

src/proxy/tests/client_masking_shape_classifier_fuzz_redteam_expected_fail_tests.rs

@@ -19,6 +19,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,

src/proxy/tests/client_masking_shape_hardening_adversarial_tests.rs

@@ -19,6 +19,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,

src/proxy/tests/client_masking_shape_hardening_redteam_expected_fail_tests.rs

@@ -19,6 +19,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,

src/proxy/tests/client_masking_shape_hardening_security_tests.rs

@@ -19,6 +19,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,

src/proxy/tests/client_masking_stress_adversarial_tests.rs

@@ -33,6 +33,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -79,17 +80,72 @@ fn make_valid_tls_client_hello(secret: &[u8], timestamp: u32, tls_len: usize, fi
         "TLS length must fit into record header"
     );
 
-    let total_len = 5 + tls_len;
-    let mut handshake = vec![fill; total_len];
-
-    handshake[0] = 0x16;
-    handshake[1] = 0x03;
-    handshake[2] = 0x01;
-    handshake[3..5].copy_from_slice(&(tls_len as u16).to_be_bytes());
-
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const TLS_EXTENSION_PADDING: u16 = 0x0015;
+    const X25519_KEY_SHARE_LEN: usize = 32;
     let session_id_len: usize = 32;
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
 
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let base_tls_len = 4
+        + 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    assert!(
+        tls_len == base_tls_len || tls_len >= base_tls_len + 4,
+        "TLS length must leave room for a complete padding extension"
+    );
+    if tls_len > base_tls_len {
+        let padding_len = tls_len - base_tls_len - 4;
+        extensions.extend_from_slice(&TLS_EXTENSION_PADDING.to_be_bytes());
+        extensions.extend_from_slice(&(padding_len as u16).to_be_bytes());
+        extensions.resize(extensions.len() + padding_len, fill);
+    }
+
+    let body_len = tls_len - 4;
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + tls_len);
+    handshake.push(0x16);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&(tls_len as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
     handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
     let computed = sha256_hmac(secret, &handshake);
     let mut digest = computed;
@@ -204,8 +260,13 @@ async fn run_parallel_tail_fallback_case(
             assert_eq!(server_hello_head[0], 0x16);
             read_tls_record_body(&mut client_side, server_hello_head).await;
 
-            client_side.write_all(&invalid_mtproto).await.unwrap();
-            for chunk in trailing.chunks(write_chunk.max(1)) {
+            let mut chunks = trailing.chunks(write_chunk.max(1));
+            let mut client_payload = invalid_mtproto;
+            if let Some(first_chunk) = chunks.next() {
+                client_payload.extend_from_slice(first_chunk);
+            }
+            client_side.write_all(&client_payload).await.unwrap();
+            for chunk in chunks {
                 client_side.write_all(chunk).await.unwrap();
             }
             client_side.shutdown().await.unwrap();

src/proxy/tests/client_security_tests.rs

@@ -3,7 +3,7 @@ use crate::config::{UpstreamConfig, UpstreamType};
 use crate::crypto::{AesCtr, sha256, sha256_hmac};
 use crate::protocol::constants::{
     DC_IDX_POS, HANDSHAKE_LEN, IV_LEN, PREKEY_LEN, PROTO_TAG_POS, ProtoTag, SKIP_LEN,
-    TLS_RECORD_CHANGE_CIPHER,
+    TLS_RECORD_CHANGE_CIPHER, TLS_VERSION,
 };
 use crate::protocol::tls;
 use crate::proxy::handshake::HandshakeSuccess;
@@ -341,6 +341,7 @@ async fn relay_task_abort_releases_user_gate_and_ip_reservation() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -459,6 +460,7 @@ async fn relay_cutover_releases_user_gate_and_ip_reservation() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -586,6 +588,7 @@ async fn integration_route_cutover_and_quota_overlap_fails_closed_and_releases_s
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -759,6 +762,7 @@ async fn proxy_protocol_header_is_rejected_when_trust_list_is_empty() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -839,6 +843,7 @@ async fn proxy_protocol_header_from_untrusted_peer_range_is_rejected_under_load(
                 selected_scope: String::new(),
                 ipv4: None,
                 ipv6: None,
+                prefer: None,
             }],
             1,
             1,
@@ -1032,6 +1037,7 @@ async fn short_tls_probe_is_masked_through_client_pipeline() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -1123,6 +1129,7 @@ async fn tls12_record_probe_is_masked_through_client_pipeline() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -1212,6 +1219,7 @@ async fn handle_client_stream_increments_connects_all_exactly_once() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -1308,6 +1316,7 @@ async fn running_client_handler_increments_connects_all_exactly_once() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -1401,6 +1410,7 @@ async fn idle_pooled_connection_closes_cleanly_in_generic_stream_path() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -1475,6 +1485,7 @@ async fn idle_pooled_connection_closes_cleanly_in_client_handler_path() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -1564,6 +1575,7 @@ async fn partial_tls_header_stall_triggers_handshake_timeout() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -1618,17 +1630,73 @@ fn make_valid_tls_client_hello_with_len(secret: &[u8], timestamp: u32, tls_len:
         "TLS length must fit into record header"
     );
 
-    let total_len = 5 + tls_len;
-    let mut handshake = vec![0x42u8; total_len];
-
-    handshake[0] = 0x16;
-    handshake[1] = 0x03;
-    handshake[2] = 0x01;
-    handshake[3..5].copy_from_slice(&(tls_len as u16).to_be_bytes());
-
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const TLS_EXTENSION_PADDING: u16 = 0x0015;
+    const X25519_KEY_SHARE_LEN: usize = 32;
+    let fill = 0x42u8;
     let session_id_len: usize = 32;
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
 
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let base_tls_len = 4
+        + 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    assert!(
+        tls_len == base_tls_len || tls_len >= base_tls_len + 4,
+        "TLS length must leave room for a complete padding extension"
+    );
+    if tls_len > base_tls_len {
+        let padding_len = tls_len - base_tls_len - 4;
+        extensions.extend_from_slice(&TLS_EXTENSION_PADDING.to_be_bytes());
+        extensions.extend_from_slice(&(padding_len as u16).to_be_bytes());
+        extensions.resize(extensions.len() + padding_len, fill);
+    }
+
+    let body_len = tls_len - 4;
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + tls_len);
+    handshake.push(0x16);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&(tls_len as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
     handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
     let computed = sha256_hmac(secret, &handshake);
     let mut digest = computed;
@@ -1651,6 +1719,9 @@ fn make_valid_tls_client_hello_with_alpn(
     timestamp: u32,
     alpn_protocols: &[&[u8]],
 ) -> Vec<u8> {
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const X25519_KEY_SHARE_LEN: usize = 32;
+
     let mut body = Vec::new();
     body.extend_from_slice(&TLS_VERSION);
     body.extend_from_slice(&[0u8; 32]);
@@ -1662,6 +1733,19 @@ fn make_valid_tls_client_hello_with_alpn(
     body.push(0);
 
     let mut ext_blob = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    ext_blob.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    ext_blob.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    ext_blob.extend_from_slice(&key_share_extension);
+
     if !alpn_protocols.is_empty() {
         let mut alpn_list = Vec::new();
         for proto in alpn_protocols {
@@ -1892,6 +1976,7 @@ async fn valid_tls_path_does_not_fall_back_to_mask_backend() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -2004,6 +2089,7 @@ async fn valid_tls_with_invalid_mtproto_falls_back_to_mask_backend() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -2048,8 +2134,9 @@ async fn valid_tls_with_invalid_mtproto_falls_back_to_mask_backend() {
         .unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client_side.write_all(&tls_app_record).await.unwrap();
-    client_side.write_all(&trailing_tls_record).await.unwrap();
+    let mut client_payload = tls_app_record;
+    client_payload.extend_from_slice(&trailing_tls_record);
+    client_side.write_all(&client_payload).await.unwrap();
 
     tokio::time::timeout(Duration::from_secs(3), accept_task)
         .await
@@ -2114,6 +2201,7 @@ async fn client_handler_tls_bad_mtproto_is_forwarded_to_mask_backend() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -2173,8 +2261,9 @@ async fn client_handler_tls_bad_mtproto_is_forwarded_to_mask_backend() {
     client.read_exact(&mut tls_response_head).await.unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client.write_all(&tls_app_record).await.unwrap();
-    client.write_all(&trailing_tls_record).await.unwrap();
+    let mut client_payload = tls_app_record;
+    client_payload.extend_from_slice(&trailing_tls_record);
+    client.write_all(&client_payload).await.unwrap();
 
     tokio::time::timeout(Duration::from_secs(3), mask_accept_task)
         .await
@@ -2239,6 +2328,7 @@ async fn alpn_mismatch_tls_probe_is_masked_through_client_pipeline() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -2335,6 +2425,7 @@ async fn invalid_hmac_tls_probe_is_masked_through_client_pipeline() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -2437,6 +2528,7 @@ async fn burst_invalid_tls_probes_are_masked_verbatim() {
                 selected_scope: String::new(),
                 ipv4: None,
                 ipv6: None,
+                prefer: None,
             }],
             1,
             1,
@@ -3395,6 +3487,7 @@ async fn relay_connect_error_releases_user_and_ip_before_return() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -3963,6 +4056,7 @@ async fn untrusted_proxy_header_source_is_rejected() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -4036,6 +4130,7 @@ async fn empty_proxy_trusted_cidrs_rejects_proxy_header_by_default() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -4136,6 +4231,7 @@ async fn oversized_tls_record_is_masked_in_generic_stream_pipeline() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -4242,6 +4338,7 @@ async fn oversized_tls_record_is_masked_in_client_handler_pipeline() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -4362,6 +4459,7 @@ async fn tls_record_len_min_minus_1_is_rejected_in_generic_stream_pipeline() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -4468,6 +4566,7 @@ async fn tls_record_len_min_minus_1_is_rejected_in_client_handler_pipeline() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -4577,6 +4676,7 @@ async fn tls_record_len_16384_is_accepted_in_generic_stream_pipeline() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -4681,6 +4781,7 @@ async fn tls_record_len_16384_is_accepted_in_client_handler_pipeline() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,

src/proxy/tests/client_timing_profile_adversarial_tests.rs

@@ -32,6 +32,7 @@ fn make_test_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -74,12 +75,17 @@ async fn run_generic_once(class: ProbeClass) -> u128 {
     let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
     let backend_addr = listener.local_addr().unwrap();
     let backend_reply = REPLY_404.to_vec();
+    let probe = match class {
+        ProbeClass::MalformedTlsTruncation => malformed_tls_probe(),
+        ProbeClass::PlainWebBaseline => plain_web_probe(),
+    };
 
     let accept_task = tokio::spawn({
         let backend_reply = backend_reply.clone();
+        let expected_probe_len = probe.len();
         async move {
             let (mut stream, _) = listener.accept().await.unwrap();
-            let mut buf = [0u8; 5];
+            let mut buf = vec![0u8; expected_probe_len];
             stream.read_exact(&mut buf).await.unwrap();
             stream.write_all(&backend_reply).await.unwrap();
         }
@@ -93,6 +99,7 @@ async fn run_generic_once(class: ProbeClass) -> u128 {
     cfg.censorship.mask_host = Some("127.0.0.1".to_string());
     cfg.censorship.mask_port = backend_addr.port();
     cfg.censorship.mask_proxy_protocol = 0;
+    cfg.censorship.mask_shape_hardening = false;
 
     if matches!(class, ProbeClass::PlainWebBaseline) {
         cfg.general.modes.classic = false;
@@ -129,11 +136,6 @@ async fn run_generic_once(class: ProbeClass) -> u128 {
         false,
     ));
 
-    let probe = match class {
-        ProbeClass::MalformedTlsTruncation => malformed_tls_probe(),
-        ProbeClass::PlainWebBaseline => plain_web_probe(),
-    };
-
     let started = Instant::now();
     client_side.write_all(&probe).await.unwrap();
     client_side.shutdown().await.unwrap();
@@ -169,11 +171,16 @@ async fn run_client_handler_once(class: ProbeClass) -> u128 {
     let front_addr = front_listener.local_addr().unwrap();
 
     let backend_reply = REPLY_404.to_vec();
+    let probe = match class {
+        ProbeClass::MalformedTlsTruncation => malformed_tls_probe(),
+        ProbeClass::PlainWebBaseline => plain_web_probe(),
+    };
     let mask_accept_task = tokio::spawn({
         let backend_reply = backend_reply.clone();
+        let expected_probe_len = probe.len();
         async move {
             let (mut stream, _) = mask_listener.accept().await.unwrap();
-            let mut buf = [0u8; 5];
+            let mut buf = vec![0u8; expected_probe_len];
             stream.read_exact(&mut buf).await.unwrap();
             stream.write_all(&backend_reply).await.unwrap();
         }
@@ -187,6 +194,7 @@ async fn run_client_handler_once(class: ProbeClass) -> u128 {
     cfg.censorship.mask_host = Some("127.0.0.1".to_string());
     cfg.censorship.mask_port = backend_addr.port();
     cfg.censorship.mask_proxy_protocol = 0;
+    cfg.censorship.mask_shape_hardening = false;
 
     if matches!(class, ProbeClass::PlainWebBaseline) {
         cfg.general.modes.classic = false;
@@ -239,11 +247,6 @@ async fn run_client_handler_once(class: ProbeClass) -> u128 {
         })
     };
 
-    let probe = match class {
-        ProbeClass::MalformedTlsTruncation => malformed_tls_probe(),
-        ProbeClass::PlainWebBaseline => plain_web_probe(),
-    };
-
     let mut client = TcpStream::connect(front_addr).await.unwrap();
     let started = Instant::now();
     client.write_all(&probe).await.unwrap();

src/proxy/tests/client_tls_clienthello_size_security_tests.rs

@@ -34,6 +34,7 @@ fn make_test_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,

src/proxy/tests/client_tls_clienthello_truncation_adversarial_tests.rs

@@ -35,6 +35,7 @@ fn make_test_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,

src/proxy/tests/client_tls_mtproto_fallback_security_tests.rs

@@ -49,6 +49,7 @@ fn build_harness(secret_hex: &str, mask_port: u16) -> PipelineHarness {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -78,17 +79,72 @@ fn make_valid_tls_client_hello(secret: &[u8], timestamp: u32, tls_len: usize, fi
         "TLS length must fit into record header"
     );
 
-    let total_len = 5 + tls_len;
-    let mut handshake = vec![fill; total_len];
-
-    handshake[0] = 0x16;
-    handshake[1] = 0x03;
-    handshake[2] = 0x01;
-    handshake[3..5].copy_from_slice(&(tls_len as u16).to_be_bytes());
-
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const TLS_EXTENSION_PADDING: u16 = 0x0015;
+    const X25519_KEY_SHARE_LEN: usize = 32;
     let session_id_len: usize = 32;
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
 
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let base_tls_len = 4
+        + 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    assert!(
+        tls_len == base_tls_len || tls_len >= base_tls_len + 4,
+        "TLS length must leave room for a complete padding extension"
+    );
+    if tls_len > base_tls_len {
+        let padding_len = tls_len - base_tls_len - 4;
+        extensions.extend_from_slice(&TLS_EXTENSION_PADDING.to_be_bytes());
+        extensions.extend_from_slice(&(padding_len as u16).to_be_bytes());
+        extensions.resize(extensions.len() + padding_len, fill);
+    }
+
+    let body_len = tls_len - 4;
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + tls_len);
+    handshake.push(0x16);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&(tls_len as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
     handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
     let computed = sha256_hmac(secret, &handshake);
     let mut digest = computed;
@@ -190,11 +246,9 @@ async fn tls_bad_mtproto_fallback_preserves_wire_and_backend_response() {
     assert_eq!(tls_response_head[0], 0x16);
     read_and_discard_tls_record_body(&mut client_side, tls_response_head).await;
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    client_side.write_all(&trailing_record).await.unwrap();
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&trailing_record);
+    client_side.write_all(&client_payload).await.unwrap();
 
     tokio::time::timeout(Duration::from_secs(3), accept_task)
         .await
@@ -260,11 +314,9 @@ async fn tls_bad_mtproto_fallback_keeps_connects_bad_accounting() {
         .unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    client_side.write_all(&trailing_record).await.unwrap();
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&trailing_record);
+    client_side.write_all(&client_payload).await.unwrap();
 
     tokio::time::timeout(Duration::from_secs(3), accept_task)
         .await
@@ -334,11 +386,9 @@ async fn tls_bad_mtproto_fallback_forwards_zero_length_tls_record_verbatim() {
         .unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    client_side.write_all(&trailing_record).await.unwrap();
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&trailing_record);
+    client_side.write_all(&client_payload).await.unwrap();
 
     tokio::time::timeout(Duration::from_secs(3), accept_task)
         .await
@@ -402,11 +452,9 @@ async fn tls_bad_mtproto_fallback_forwards_max_tls_record_verbatim() {
         .unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    client_side.write_all(&trailing_record).await.unwrap();
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&trailing_record);
+    client_side.write_all(&client_payload).await.unwrap();
 
     tokio::time::timeout(Duration::from_secs(3), accept_task)
         .await
@@ -480,11 +528,9 @@ async fn tls_bad_mtproto_fallback_light_fuzz_tls_record_lengths_verbatim() {
             .unwrap();
         assert_eq!(tls_response_head[0], 0x16);
 
-        client_side
-            .write_all(&invalid_mtproto_record)
-            .await
-            .unwrap();
-        client_side.write_all(&trailing_record).await.unwrap();
+        let mut client_payload = invalid_mtproto_record;
+        client_payload.extend_from_slice(&trailing_record);
+        client_side.write_all(&client_payload).await.unwrap();
 
         tokio::time::timeout(Duration::from_secs(3), accept_task)
             .await
@@ -585,11 +631,9 @@ async fn tls_bad_mtproto_fallback_concurrent_sessions_are_isolated() {
                 .unwrap();
             assert_eq!(tls_response_head[0], 0x16);
 
-            client_side
-                .write_all(&invalid_mtproto_record)
-                .await
-                .unwrap();
-            client_side.write_all(&trailing_record).await.unwrap();
+            let mut client_payload = invalid_mtproto_record;
+            client_payload.extend_from_slice(&trailing_record);
+            client_side.write_all(&client_payload).await.unwrap();
 
             drop(client_side);
             let _ = tokio::time::timeout(Duration::from_secs(3), handler)
@@ -659,12 +703,14 @@ async fn tls_bad_mtproto_fallback_forwards_fragmented_client_writes_verbatim() {
         .unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
+    let mut chunks = trailing_record.chunks(3);
+    let mut client_payload = invalid_mtproto_record;
+    if let Some(first_chunk) = chunks.next() {
+        client_payload.extend_from_slice(first_chunk);
+    }
+    client_side.write_all(&client_payload).await.unwrap();
 
-    for chunk in trailing_record.chunks(3) {
+    for chunk in chunks {
         client_side.write_all(chunk).await.unwrap();
     }
 
@@ -728,11 +774,13 @@ async fn tls_bad_mtproto_fallback_header_fragmentation_bytewise_is_verbatim() {
         .unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    for b in trailing_record.iter().copied() {
+    let mut bytes = trailing_record.iter().copied();
+    let mut client_payload = invalid_mtproto_record;
+    if let Some(first_byte) = bytes.next() {
+        client_payload.push(first_byte);
+    }
+    client_side.write_all(&client_payload).await.unwrap();
+    for b in bytes {
         client_side.write_all(&[b]).await.unwrap();
     }
 
@@ -801,14 +849,16 @@ async fn tls_bad_mtproto_fallback_record_splitting_chaos_is_verbatim() {
         .unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-
     let chaos = [7usize, 1, 19, 3, 5, 31, 2, 11, 13, 17];
     let mut pos = 0usize;
     let mut idx = 0usize;
+    let mut client_payload = invalid_mtproto_record;
+    let first_step = chaos[idx % chaos.len()];
+    let first_end = first_step.min(trailing_record.len());
+    client_payload.extend_from_slice(&trailing_record[..first_end]);
+    client_side.write_all(&client_payload).await.unwrap();
+    pos = first_end;
+    idx += 1;
     while pos < trailing_record.len() {
         let step = chaos[idx % chaos.len()];
         let end = (pos + step).min(trailing_record.len());
@@ -883,11 +933,9 @@ async fn tls_bad_mtproto_fallback_multiple_tls_records_are_forwarded_in_order()
         .unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    client_side.write_all(&r1).await.unwrap();
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&r1);
+    client_side.write_all(&client_payload).await.unwrap();
     client_side.write_all(&r2).await.unwrap();
     client_side.write_all(&r3).await.unwrap();
 
@@ -957,11 +1005,9 @@ async fn tls_bad_mtproto_fallback_client_half_close_propagates_eof_to_backend()
         .unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    client_side.write_all(&trailing_record).await.unwrap();
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&trailing_record);
+    client_side.write_all(&client_payload).await.unwrap();
     client_side.shutdown().await.unwrap();
 
     tokio::time::timeout(Duration::from_secs(3), accept_task)
@@ -1028,11 +1074,9 @@ async fn tls_bad_mtproto_fallback_backend_half_close_after_response_is_tolerated
     assert_eq!(tls_response_head[0], 0x16);
     read_and_discard_tls_record_body(&mut client_side, tls_response_head).await;
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    client_side.write_all(&trailing_record).await.unwrap();
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&trailing_record);
+    client_side.write_all(&client_payload).await.unwrap();
 
     tokio::time::timeout(Duration::from_secs(3), accept_task)
         .await
@@ -1089,11 +1133,9 @@ async fn tls_bad_mtproto_fallback_backend_reset_after_clienthello_is_handled() {
         .unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    let write_res = client_side.write_all(&trailing_record).await;
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&trailing_record);
+    let write_res = client_side.write_all(&client_payload).await;
     assert!(
         write_res.is_ok() || write_res.is_err(),
         "write completion is environment dependent under backend reset"
@@ -1169,11 +1211,9 @@ async fn tls_bad_mtproto_fallback_backend_slow_reader_preserves_byte_identity()
         .unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    client_side.write_all(&trailing_record).await.unwrap();
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&trailing_record);
+    client_side.write_all(&client_payload).await.unwrap();
 
     tokio::time::timeout(Duration::from_secs(5), accept_task)
         .await
@@ -1253,11 +1293,9 @@ async fn tls_bad_mtproto_fallback_replay_pressure_masks_replay_without_serverhel
                 let mut head = [0u8; 5];
                 client_side.read_exact(&mut head).await.unwrap();
                 assert_eq!(head[0], 0x16);
-                client_side
-                    .write_all(&invalid_mtproto_record)
-                    .await
-                    .unwrap();
-                client_side.write_all(&trailing_record).await.unwrap();
+                let mut client_payload = invalid_mtproto_record;
+                client_payload.extend_from_slice(&trailing_record);
+                client_side.write_all(&client_payload).await.unwrap();
             } else {
                 let mut one = [0u8; 1];
                 let no_server_hello = tokio::time::timeout(
@@ -1351,13 +1389,29 @@ async fn tls_bad_mtproto_fallback_large_multi_record_chaos_under_backpressure()
         .unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-
     let chaos = [5usize, 23, 11, 47, 3, 19, 29, 13, 7, 31];
-    for record in [&a, &b, &c] {
+    let records = [&a, &b, &c];
+    let mut records_iter = records.iter().copied();
+    let mut client_payload = invalid_mtproto_record;
+    if let Some(first_record) = records_iter.next() {
+        let first_step = chaos[0].min(first_record.len());
+        client_payload.extend_from_slice(&first_record[..first_step]);
+        client_side.write_all(&client_payload).await.unwrap();
+
+        let mut pos = first_step;
+        let mut idx = 1usize;
+        while pos < first_record.len() {
+            let step = chaos[idx % chaos.len()];
+            let end = (pos + step).min(first_record.len());
+            client_side
+                .write_all(&first_record[pos..end])
+                .await
+                .unwrap();
+            pos = end;
+            idx += 1;
+        }
+    }
+    for record in records_iter {
         let mut pos = 0usize;
         let mut idx = 0usize;
         while pos < record.len() {
@@ -1432,11 +1486,9 @@ async fn tls_bad_mtproto_fallback_interleaved_control_and_application_records_ve
         .unwrap();
     assert_eq!(tls_response_head[0], 0x16);
 
-    client_side
-        .write_all(&invalid_mtproto_record)
-        .await
-        .unwrap();
-    client_side.write_all(&ccs).await.unwrap();
+    let mut client_payload = invalid_mtproto_record;
+    client_payload.extend_from_slice(&ccs);
+    client_side.write_all(&client_payload).await.unwrap();
     client_side.write_all(&app).await.unwrap();
     client_side.write_all(&alert).await.unwrap();
 
@@ -1532,11 +1584,13 @@ async fn tls_bad_mtproto_fallback_many_short_sessions_with_chaos_no_cross_leak()
             client_side.read_exact(&mut head).await.unwrap();
             assert_eq!(head[0], 0x16);
 
-            client_side
-                .write_all(&invalid_mtproto_record)
-                .await
-                .unwrap();
-            for chunk in record.chunks((idx % 9) + 1) {
+            let mut chunks = record.chunks((idx % 9) + 1);
+            let mut client_payload = invalid_mtproto_record;
+            if let Some(first_chunk) = chunks.next() {
+                client_payload.extend_from_slice(first_chunk);
+            }
+            client_side.write_all(&client_payload).await.unwrap();
+            for chunk in chunks {
                 client_side.write_all(chunk).await.unwrap();
             }
 

src/proxy/tests/direct_relay_security_tests.rs

@@ -1338,6 +1338,7 @@ async fn direct_relay_abort_midflight_releases_route_gauge() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -1448,6 +1449,7 @@ async fn direct_relay_cutover_midflight_releases_route_gauge() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -1570,6 +1572,7 @@ async fn direct_relay_cutover_storm_multi_session_keeps_generic_errors_and_relea
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,
@@ -1803,6 +1806,7 @@ async fn negative_direct_relay_dc_connection_refused_fails_fast() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         100,
@@ -1897,6 +1901,7 @@ async fn adversarial_direct_relay_cutover_integrity() {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         100,

src/proxy/tests/handshake_advanced_clever_tests.rs

@@ -21,11 +21,59 @@ fn test_config_with_secret_hex(secret_hex: &str) -> ProxyConfig {
 }
 
 fn make_valid_tls_handshake(secret: &[u8], timestamp: u32) -> Vec<u8> {
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const X25519_KEY_SHARE_LEN: usize = 32;
     let session_id_len: usize = 32;
-    let len = tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN + 1 + session_id_len;
-    let mut handshake = vec![0x42u8; len];
+    let fill = 0x42u8;
 
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let body_len = 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + 4 + body_len);
+    handshake.push(TLS_RECORD_HANDSHAKE);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&((4 + body_len) as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
     handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
 
     let computed = sha256_hmac(secret, &handshake);
@@ -85,6 +133,9 @@ fn make_valid_tls_client_hello_with_alpn(
     timestamp: u32,
     alpn_protocols: &[&[u8]],
 ) -> Vec<u8> {
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const X25519_KEY_SHARE_LEN: usize = 32;
+
     let mut body = Vec::new();
     body.extend_from_slice(&TLS_VERSION);
     body.extend_from_slice(&[0u8; 32]);
@@ -96,6 +147,19 @@ fn make_valid_tls_client_hello_with_alpn(
     body.push(0);
 
     let mut ext_blob = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    ext_blob.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    ext_blob.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    ext_blob.extend_from_slice(&key_share_extension);
+
     if !alpn_protocols.is_empty() {
         let mut alpn_list = Vec::new();
         for proto in alpn_protocols {
@@ -150,13 +214,7 @@ async fn tls_minimum_viable_length_boundary() {
     let rng = SecureRandom::new();
     let peer: SocketAddr = "192.0.2.1:12345".parse().unwrap();
 
-    let min_len = tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN + 1;
-    let mut exact_min_handshake = vec![0x42u8; min_len];
-    exact_min_handshake[min_len - 1] = 0;
-    exact_min_handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
-    let digest = sha256_hmac(&secret, &exact_min_handshake);
-    exact_min_handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN]
-        .copy_from_slice(&digest);
+    let exact_min_handshake = make_valid_tls_handshake(&secret, 0);
 
     let res = handle_tls_handshake(
         &exact_min_handshake,
@@ -171,12 +229,12 @@ async fn tls_minimum_viable_length_boundary() {
     .await;
     assert!(
         matches!(res, HandshakeResult::Success(_)),
-        "Exact minimum length TLS handshake must succeed"
+        "Minimum valid TLS ClientHello must succeed"
     );
 
-    let short_handshake = vec![0x42u8; min_len - 1];
+    let short_handshake = &exact_min_handshake[..exact_min_handshake.len() - 1];
     let res_short = handle_tls_handshake(
-        &short_handshake,
+        short_handshake,
         tokio::io::empty(),
         tokio::io::sink(),
         peer,
@@ -188,7 +246,7 @@ async fn tls_minimum_viable_length_boundary() {
     .await;
     assert!(
         matches!(res_short, HandshakeResult::BadClient { .. }),
-        "Handshake 1 byte shorter than minimum must fail closed"
+        "Handshake 1 byte shorter than minimum valid ClientHello must fail closed"
     );
 }
 

src/proxy/tests/handshake_baseline_invariant_tests.rs

@@ -1,5 +1,6 @@
 use super::*;
 use crate::crypto::sha256_hmac;
+use crate::protocol::constants::{TLS_RECORD_HANDSHAKE, TLS_VERSION};
 use crate::stats::ReplayChecker;
 use std::net::{IpAddr, Ipv4Addr, SocketAddr};
 use std::time::{Duration, Instant};
@@ -17,11 +18,59 @@ fn test_config_with_secret_hex(secret_hex: &str) -> ProxyConfig {
 }
 
 fn make_valid_tls_handshake(secret: &[u8], timestamp: u32) -> Vec<u8> {
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const X25519_KEY_SHARE_LEN: usize = 32;
     let session_id_len: usize = 32;
-    let len = tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN + 1 + session_id_len;
-    let mut handshake = vec![0x42u8; len];
+    let fill = 0x42u8;
 
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let body_len = 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + 4 + body_len);
+    handshake.push(TLS_RECORD_HANDSHAKE);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&((4 + body_len) as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
     handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
 
     let computed = sha256_hmac(secret, &handshake);

src/proxy/tests/handshake_more_clever_tests.rs

@@ -25,11 +25,59 @@ fn test_config_with_secret_hex(secret_hex: &str) -> ProxyConfig {
 }
 
 fn make_valid_tls_handshake(secret: &[u8], timestamp: u32) -> Vec<u8> {
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const X25519_KEY_SHARE_LEN: usize = 32;
     let session_id_len: usize = 32;
-    let len = tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN + 1 + session_id_len;
-    let mut handshake = vec![0x42u8; len];
+    let fill = 0x42u8;
 
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let body_len = 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + 4 + body_len);
+    handshake.push(TLS_RECORD_HANDSHAKE);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&((4 + body_len) as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
     handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
 
     let computed = sha256_hmac(secret, &handshake);
@@ -90,6 +138,9 @@ fn make_valid_tls_client_hello_with_sni_and_alpn(
     sni_host: &str,
     alpn_protocols: &[&[u8]],
 ) -> Vec<u8> {
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const X25519_KEY_SHARE_LEN: usize = 32;
+
     let mut body = Vec::new();
     body.extend_from_slice(&TLS_VERSION);
     body.extend_from_slice(&[0u8; 32]);
@@ -112,6 +163,19 @@ fn make_valid_tls_client_hello_with_sni_and_alpn(
     ext_blob.extend_from_slice(&(sni_payload.len() as u16).to_be_bytes());
     ext_blob.extend_from_slice(&sni_payload);
 
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    ext_blob.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    ext_blob.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    ext_blob.extend_from_slice(&key_share_extension);
+
     if !alpn_protocols.is_empty() {
         let mut alpn_list = Vec::new();
         for proto in alpn_protocols {

src/proxy/tests/handshake_real_bug_stress_tests.rs

@@ -24,6 +24,9 @@ fn make_valid_tls_client_hello_with_alpn(
     timestamp: u32,
     alpn_protocols: &[&[u8]],
 ) -> Vec<u8> {
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const X25519_KEY_SHARE_LEN: usize = 32;
+
     let mut body = Vec::new();
     body.extend_from_slice(&TLS_VERSION);
     body.extend_from_slice(&[0u8; 32]);
@@ -35,6 +38,19 @@ fn make_valid_tls_client_hello_with_alpn(
     body.push(0);
 
     let mut ext_blob = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    ext_blob.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    ext_blob.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    ext_blob.extend_from_slice(&key_share_extension);
+
     if !alpn_protocols.is_empty() {
         let mut alpn_list = Vec::new();
         for proto in alpn_protocols {

src/proxy/tests/handshake_security_tests.rs

@@ -10,11 +10,62 @@ use std::time::{Duration, Instant};
 use tokio::sync::Barrier;
 
 fn make_valid_tls_handshake(secret: &[u8], timestamp: u32) -> Vec<u8> {
-    let session_id_len: usize = 32;
-    let len = tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN + 1 + session_id_len;
-    let mut handshake = vec![0x42u8; len];
+    make_valid_tls_handshake_with_fill(secret, timestamp, 0x42)
+}
 
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
+fn make_valid_tls_handshake_with_fill(secret: &[u8], timestamp: u32, fill: u8) -> Vec<u8> {
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const X25519_KEY_SHARE_LEN: usize = 32;
+    let session_id_len: usize = 32;
+
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let body_len = 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + 4 + body_len);
+    handshake.push(TLS_RECORD_HANDSHAKE);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&((4 + body_len) as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
     handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
 
     let computed = sha256_hmac(secret, &handshake);
@@ -34,6 +85,9 @@ fn make_valid_tls_client_hello_with_alpn(
     timestamp: u32,
     alpn_protocols: &[&[u8]],
 ) -> Vec<u8> {
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const X25519_KEY_SHARE_LEN: usize = 32;
+
     let mut body = Vec::new();
     body.extend_from_slice(&TLS_VERSION);
     body.extend_from_slice(&[0u8; 32]);
@@ -45,6 +99,19 @@ fn make_valid_tls_client_hello_with_alpn(
     body.push(0);
 
     let mut ext_blob = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    ext_blob.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    ext_blob.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    ext_blob.extend_from_slice(&key_share_extension);
+
     if !alpn_protocols.is_empty() {
         let mut alpn_list = Vec::new();
         for proto in alpn_protocols {
@@ -92,6 +159,9 @@ fn make_valid_tls_client_hello_with_sni_and_alpn(
     sni_host: &str,
     alpn_protocols: &[&[u8]],
 ) -> Vec<u8> {
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const X25519_KEY_SHARE_LEN: usize = 32;
+
     let mut body = Vec::new();
     body.extend_from_slice(&TLS_VERSION);
     body.extend_from_slice(&[0u8; 32]);
@@ -114,6 +184,19 @@ fn make_valid_tls_client_hello_with_sni_and_alpn(
     ext_blob.extend_from_slice(&(sni_payload.len() as u16).to_be_bytes());
     ext_blob.extend_from_slice(&sni_payload);
 
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    ext_blob.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    ext_blob.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    ext_blob.extend_from_slice(&key_share_extension);
+
     if !alpn_protocols.is_empty() {
         let mut alpn_list = Vec::new();
         for proto in alpn_protocols {
@@ -549,25 +632,6 @@ async fn adversarial_tls_replay_churn_allows_only_unique_digests() {
     let replay_checker = Arc::new(ReplayChecker::new(8192, Duration::from_secs(60)));
     let rng = Arc::new(SecureRandom::new());
 
-    let make_tagged_handshake = |timestamp: u32, tag: u8| {
-        let session_id_len: usize = 32;
-        let len = tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN + 1 + session_id_len;
-        let mut handshake = vec![tag; len];
-
-        handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
-        handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
-        let computed = sha256_hmac(&secret, &handshake);
-        let mut digest = computed;
-        let ts = timestamp.to_le_bytes();
-        for i in 0..4 {
-            digest[28 + i] ^= ts[i];
-        }
-
-        handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN]
-            .copy_from_slice(&digest);
-        handshake
-    };
-
     let mut tasks = Vec::new();
 
     // 128 exact duplicates: only one should pass.
@@ -596,12 +660,17 @@ async fn adversarial_tls_replay_churn_allows_only_unique_digests() {
         }));
     }
 
-    // 128 unique timestamps: all should pass because HMAC digest differs.
+    // 128 unique ClientHello bodies: all should pass because replay tracks the
+    // first digest half, while timestamp skew is encoded in the last bytes.
     for i in 0..128u16 {
         let config = Arc::clone(&config);
         let replay_checker = Arc::clone(&replay_checker);
         let rng = Arc::clone(&rng);
-        let handshake = make_tagged_handshake(10_000 + i as u32, (i as u8).wrapping_add(0x80));
+        let handshake = make_valid_tls_handshake_with_fill(
+            &secret,
+            10_000 + i as u32,
+            (i as u8).wrapping_add(0x80),
+        );
         tasks.push(tokio::spawn(async move {
             let peer = SocketAddr::new(
                 IpAddr::V4(Ipv4Addr::new(198, 18, 0, ((i % 250) + 1) as u8)),

src/proxy/tests/handshake_timing_manual_bench_tests.rs

@@ -47,11 +47,59 @@ fn make_valid_mtproto_handshake(
 }
 
 fn make_valid_tls_handshake(secret: &[u8], timestamp: u32) -> Vec<u8> {
+    const TLS_AES_128_GCM_SHA256: [u8; 2] = [0x13, 0x01];
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const X25519_KEY_SHARE_LEN: usize = 32;
     let session_id_len: usize = 32;
-    let len = tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN + 1 + session_id_len;
-    let mut handshake = vec![0x42u8; len];
+    let fill = 0x42u8;
 
-    handshake[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = session_id_len as u8;
+    let mut extensions = Vec::new();
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    extensions.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    extensions.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    extensions.extend_from_slice(&key_share_extension);
+
+    let body_len = 2
+        + 32
+        + 1
+        + session_id_len
+        + 2
+        + TLS_AES_128_GCM_SHA256.len()
+        + 1
+        + 1
+        + 2
+        + extensions.len();
+    let mut body = Vec::with_capacity(body_len);
+    body.extend_from_slice(&TLS_VERSION);
+    body.extend_from_slice(&[fill; 32]);
+    body.push(session_id_len as u8);
+    body.extend_from_slice(&[fill; 32]);
+    body.extend_from_slice(&(TLS_AES_128_GCM_SHA256.len() as u16).to_be_bytes());
+    body.extend_from_slice(&TLS_AES_128_GCM_SHA256);
+    body.push(1);
+    body.push(0);
+    body.extend_from_slice(&(extensions.len() as u16).to_be_bytes());
+    body.extend_from_slice(&extensions);
+    assert_eq!(body.len(), body_len);
+
+    let mut handshake = Vec::with_capacity(5 + 4 + body_len);
+    handshake.push(TLS_RECORD_HANDSHAKE);
+    handshake.extend_from_slice(&[0x03, 0x01]);
+    handshake.extend_from_slice(&((4 + body_len) as u16).to_be_bytes());
+    handshake.push(0x01);
+    let body_len_bytes = (body_len as u32).to_be_bytes();
+    handshake.extend_from_slice(&body_len_bytes[1..4]);
+    handshake.extend_from_slice(&body);
+
+    // The proxy authenticates TLS-fronted clients through the random field.
     handshake[tls::TLS_DIGEST_POS..tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN].fill(0);
 
     let computed = sha256_hmac(secret, &handshake);
@@ -72,6 +120,9 @@ fn make_valid_tls_client_hello_with_sni_and_alpn(
     sni_host: &str,
     alpn_protocols: &[&[u8]],
 ) -> Vec<u8> {
+    const TLS_EXTENSION_KEY_SHARE: u16 = 0x0033;
+    const X25519_KEY_SHARE_LEN: usize = 32;
+
     let mut body = Vec::new();
     body.extend_from_slice(&TLS_VERSION);
     body.extend_from_slice(&[0u8; 32]);
@@ -93,6 +144,19 @@ fn make_valid_tls_client_hello_with_sni_and_alpn(
     ext_blob.extend_from_slice(&(sni_payload.len() as u16).to_be_bytes());
     ext_blob.extend_from_slice(&sni_payload);
 
+    let mut key_share = Vec::new();
+    key_share.extend_from_slice(&tls::TLS_NAMED_GROUP_X25519.to_be_bytes());
+    key_share.extend_from_slice(&(X25519_KEY_SHARE_LEN as u16).to_be_bytes());
+    key_share.push(9);
+    key_share.resize(key_share.len() + X25519_KEY_SHARE_LEN - 1, 0);
+
+    let mut key_share_extension = Vec::new();
+    key_share_extension.extend_from_slice(&(key_share.len() as u16).to_be_bytes());
+    key_share_extension.extend_from_slice(&key_share);
+    ext_blob.extend_from_slice(&TLS_EXTENSION_KEY_SHARE.to_be_bytes());
+    ext_blob.extend_from_slice(&(key_share_extension.len() as u16).to_be_bytes());
+    ext_blob.extend_from_slice(&key_share_extension);
+
     if !alpn_protocols.is_empty() {
         let mut alpn_list = Vec::new();
         for proto in alpn_protocols {

src/proxy/tests/masking_additional_hardening_security_tests.rs

@@ -34,7 +34,7 @@ fn loop_guard_unspecified_bind_uses_interface_inventory() {
         "mask.example",
         443,
         local,
-        Some(resolved),
+        &[resolved],
         &interfaces,
     ));
 }

src/proxy/tests/masking_interface_cache_concurrency_security_tests.rs

@@ -25,7 +25,7 @@ async fn adversarial_parallel_cold_miss_performs_single_interface_refresh() {
         let barrier = std::sync::Arc::clone(&barrier);
         tasks.push(tokio::spawn(async move {
             barrier.wait().await;
-            is_mask_target_local_listener_async("127.0.0.1", 443, local_addr, None).await
+            is_mask_target_local_listener_async("127.0.0.1", 443, local_addr, &[]).await
         }));
     }
 

src/proxy/tests/masking_interface_cache_security_tests.rs

@@ -17,8 +17,8 @@ async fn tdd_repeated_local_listener_checks_do_not_repeat_interface_enumeration_
 
     let local_addr: SocketAddr = "0.0.0.0:443".parse().expect("valid local addr");
 
-    let _ = is_mask_target_local_listener_async("127.0.0.1", 443, local_addr, None).await;
-    let _ = is_mask_target_local_listener_async("127.0.0.1", 443, local_addr, None).await;
+    let _ = is_mask_target_local_listener_async("127.0.0.1", 443, local_addr, &[]).await;
+    let _ = is_mask_target_local_listener_async("127.0.0.1", 443, local_addr, &[]).await;
 
     assert_eq!(
         local_interface_enumerations_for_tests(),
@@ -35,7 +35,7 @@ async fn tdd_non_local_port_short_circuit_does_not_enumerate_interfaces() {
     reset_local_interface_enumerations_for_tests();
 
     let local_addr: SocketAddr = "0.0.0.0:443".parse().expect("valid local addr");
-    let is_local = is_mask_target_local_listener_async("127.0.0.1", 8443, local_addr, None).await;
+    let is_local = is_mask_target_local_listener_async("127.0.0.1", 8443, local_addr, &[]).await;
 
     assert!(
         !is_local,

src/proxy/tests/masking_relay_manual_perf_tests.rs

@@ -0,0 +1,111 @@
+use super::*;
+use std::pin::Pin;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::task::{Context, Poll};
+use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
+use tokio::time::{Duration, Instant};
+
+const PERF_TOTAL_BYTES: usize = 64 * 1024 * 1024;
+
+struct PatternReader {
+    remaining: usize,
+    chunk: usize,
+    read_calls: AtomicUsize,
+}
+
+impl PatternReader {
+    fn new(total: usize, chunk: usize) -> Self {
+        Self {
+            remaining: total,
+            chunk,
+            read_calls: AtomicUsize::new(0),
+        }
+    }
+
+    fn read_calls(&self) -> usize {
+        self.read_calls.load(Ordering::Relaxed)
+    }
+}
+
+impl AsyncRead for PatternReader {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        _cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<std::io::Result<()>> {
+        self.read_calls.fetch_add(1, Ordering::Relaxed);
+        if self.remaining == 0 {
+            return Poll::Ready(Ok(()));
+        }
+
+        let take = self.remaining.min(self.chunk).min(buf.remaining());
+        if take == 0 {
+            return Poll::Ready(Ok(()));
+        }
+
+        static PATTERN: [u8; MASK_BUFFER_MAX_SIZE] = [0xA5; MASK_BUFFER_MAX_SIZE];
+        buf.put_slice(&PATTERN[..take]);
+        self.remaining -= take;
+        Poll::Ready(Ok(()))
+    }
+}
+
+#[derive(Default)]
+struct CountingWriter {
+    written: usize,
+}
+
+impl AsyncWrite for CountingWriter {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        _cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<std::io::Result<usize>> {
+        self.written = self.written.saturating_add(buf.len());
+        Poll::Ready(Ok(buf.len()))
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<std::io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<std::io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+}
+
+#[tokio::test]
+#[ignore = "manual benchmark: throughput-sensitive and host-dependent"]
+async fn masking_copy_with_idle_timeout_manual_throughput() {
+    let mut reader = PatternReader::new(PERF_TOTAL_BYTES, MASK_BUFFER_MAX_SIZE);
+    let mut writer = CountingWriter::default();
+    let started = Instant::now();
+
+    let outcome = copy_with_idle_timeout(
+        &mut reader,
+        &mut writer,
+        PERF_TOTAL_BYTES,
+        true,
+        Duration::from_secs(30),
+    )
+    .await;
+
+    let elapsed = started.elapsed();
+    let mb = PERF_TOTAL_BYTES as f64 / (1024.0 * 1024.0);
+    let mbps = mb / elapsed.as_secs_f64();
+
+    assert_eq!(outcome.total, PERF_TOTAL_BYTES);
+    assert_eq!(writer.written, PERF_TOTAL_BYTES);
+    assert!(
+        !outcome.ended_by_eof,
+        "manual throughput run should terminate at byte cap"
+    );
+
+    eprintln!(
+        "masking manual throughput: bytes={} elapsed_ms={} mib_per_sec={:.2} read_calls={}",
+        PERF_TOTAL_BYTES,
+        elapsed.as_millis(),
+        mbps,
+        reader.read_calls()
+    );
+}

src/proxy/tests/masking_self_target_loop_security_tests.rs

@@ -15,38 +15,49 @@ fn closed_local_port() -> u16 {
 #[tokio::test]
 async fn self_target_detection_matches_literal_ipv4_listener() {
     let local: SocketAddr = "198.51.100.40:443".parse().unwrap();
-    assert!(is_mask_target_local_listener_async("198.51.100.40", 443, local, None,).await);
+    assert!(is_mask_target_local_listener_async("198.51.100.40", 443, local, &[],).await);
 }
 
 #[tokio::test]
 async fn self_target_detection_matches_bracketed_ipv6_listener() {
     let local: SocketAddr = "[2001:db8::44]:8443".parse().unwrap();
-    assert!(is_mask_target_local_listener_async("[2001:db8::44]", 8443, local, None,).await);
+    assert!(is_mask_target_local_listener_async("[2001:db8::44]", 8443, local, &[],).await);
 }
 
 #[tokio::test]
 async fn self_target_detection_keeps_same_ip_different_port_forwardable() {
     let local: SocketAddr = "203.0.113.44:443".parse().unwrap();
-    assert!(!is_mask_target_local_listener_async("203.0.113.44", 8443, local, None,).await);
+    assert!(!is_mask_target_local_listener_async("203.0.113.44", 8443, local, &[],).await);
 }
 
 #[tokio::test]
 async fn self_target_detection_normalizes_ipv4_mapped_ipv6_literal() {
     let local: SocketAddr = "127.0.0.1:443".parse().unwrap();
-    assert!(is_mask_target_local_listener_async("::ffff:127.0.0.1", 443, local, None,).await);
+    assert!(is_mask_target_local_listener_async("::ffff:127.0.0.1", 443, local, &[],).await);
 }
 
 #[tokio::test]
 async fn self_target_detection_unspecified_bind_blocks_loopback_target() {
     let local: SocketAddr = "0.0.0.0:443".parse().unwrap();
-    assert!(is_mask_target_local_listener_async("127.0.0.1", 443, local, None,).await);
+    assert!(is_mask_target_local_listener_async("127.0.0.1", 443, local, &[],).await);
 }
 
 #[tokio::test]
 async fn self_target_detection_unspecified_bind_keeps_remote_target_forwardable() {
     let local: SocketAddr = "0.0.0.0:443".parse().unwrap();
     let remote: SocketAddr = "198.51.100.44:443".parse().unwrap();
-    assert!(!is_mask_target_local_listener_async("mask.example", 443, local, Some(remote),).await);
+    assert!(!is_mask_target_local_listener_async("mask.example", 443, local, &[remote],).await);
+}
+
+#[tokio::test]
+async fn self_target_detection_checks_all_resolved_addresses() {
+    let local: SocketAddr = "127.0.0.1:443".parse().unwrap();
+    let remote: SocketAddr = "198.51.100.44:443".parse().unwrap();
+    let loopback: SocketAddr = "127.0.0.1:443".parse().unwrap();
+
+    assert!(
+        is_mask_target_local_listener_async("mask.example", 443, local, &[remote, loopback],).await
+    );
 }
 
 #[tokio::test]

src/proxy/tests/masking_timing_budget_coupling_security_tests.rs

@@ -22,6 +22,7 @@ async fn adversarial_delayed_interface_lookup_does_not_consume_outcome_floor_bud
 
     let refresh_lock = LOCAL_INTERFACE_REFRESH_LOCK.get_or_init(|| AsyncMutex::new(()));
     let held_refresh_guard = refresh_lock.lock().await;
+    reset_local_interface_enumerations_for_tests();
 
     let (mut client, server) = duplex(1024);
     let started = Instant::now();

src/proxy/tests/middle_relay_idle_registry_poison_security_tests.rs

@@ -1,33 +1,21 @@
 use super::*;
-use std::panic::{AssertUnwindSafe, catch_unwind};
 
 #[test]
-fn blackhat_registry_poison_recovers_with_fail_closed_reset_and_pressure_accounting() {
+fn blackhat_registry_stale_order_entry_is_skipped_and_pressure_accounting_continues() {
     let shared = ProxySharedState::new();
     clear_relay_idle_pressure_state_for_testing_in_shared(shared.as_ref());
 
-    let _ = catch_unwind(AssertUnwindSafe(|| {
-        let mut guard = shared
-            .middle_relay
-            .relay_idle_registry
-            .lock()
-            .expect("registry lock must be acquired before poison");
-        guard.by_conn_id.insert(
-            999,
-            RelayIdleCandidateMeta {
-                mark_order_seq: 1,
-                mark_pressure_seq: 0,
-            },
-        );
-        guard.ordered.insert((1, 999));
-        panic!("intentional poison for idle-registry recovery");
-    }));
+    shared
+        .middle_relay
+        .relay_idle_registry
+        .ordered
+        .lock()
+        .insert((0, 999));
 
-    // Helper lock must recover from poison, reset stale state, and continue.
     assert!(mark_relay_idle_candidate_for_testing(shared.as_ref(), 42));
     assert_eq!(
         oldest_relay_idle_candidate_for_testing(shared.as_ref()),
-        Some(42)
+        Some(999)
     );
 
     let before = relay_pressure_event_seq_for_testing(shared.as_ref());
@@ -35,25 +23,43 @@ fn blackhat_registry_poison_recovers_with_fail_closed_reset_and_pressure_account
     let after = relay_pressure_event_seq_for_testing(shared.as_ref());
     assert!(
         after > before,
-        "pressure accounting must still advance after poison"
+        "pressure accounting must still advance with stale ordered entries"
+    );
+
+    let mut seen_pressure_seq = before;
+    assert!(maybe_evict_idle_candidate_on_pressure_for_testing(
+        shared.as_ref(),
+        42,
+        &mut seen_pressure_seq,
+        &Stats::new()
+    ));
+    assert_eq!(
+        oldest_relay_idle_candidate_for_testing(shared.as_ref()),
+        None
     );
 
     clear_relay_idle_pressure_state_for_testing_in_shared(shared.as_ref());
 }
 
 #[test]
-fn clear_state_helper_must_reset_poisoned_registry_for_deterministic_fifo_tests() {
+fn clear_state_helper_must_reset_split_registry_for_deterministic_fifo_tests() {
     let shared = ProxySharedState::new();
     clear_relay_idle_pressure_state_for_testing_in_shared(shared.as_ref());
 
-    let _ = catch_unwind(AssertUnwindSafe(|| {
-        let _guard = shared
-            .middle_relay
-            .relay_idle_registry
-            .lock()
-            .expect("registry lock must be acquired before poison");
-        panic!("intentional poison while lock held");
-    }));
+    shared.middle_relay.relay_idle_registry.by_conn_id.insert(
+        999,
+        RelayIdleCandidateMeta {
+            mark_order_seq: 1,
+            mark_pressure_seq: 0,
+        },
+    );
+    shared
+        .middle_relay
+        .relay_idle_registry
+        .ordered
+        .lock()
+        .insert((1, 999));
+    set_relay_pressure_state_for_testing(shared.as_ref(), 7, 6);
 
     clear_relay_idle_pressure_state_for_testing_in_shared(shared.as_ref());
 

src/proxy/tests/proxy_shared_state_isolation_tests.rs

@@ -61,6 +61,7 @@ fn new_client_harness() -> ClientHarness {
             selected_scope: String::new(),
             ipv4: None,
             ipv6: None,
+            prefer: None,
         }],
         1,
         1,