diff --git a/src/proxy/handshake.rs b/src/proxy/handshake.rs
index 142495c..dbd50d5 100644
--- a/src/proxy/handshake.rs
+++ b/src/proxy/handshake.rs
@@ -11,6 +11,7 @@ use std::collections::hash_map::DefaultHasher;
 use std::hash::{Hash, Hasher};
 use std::time::{Duration, Instant};
 use dashmap::DashMap;
+use dashmap::mapref::entry::Entry;
 use tokio::io::{AsyncRead, AsyncWrite, AsyncWriteExt};
 use tracing::{debug, warn, trace};
 use zeroize::Zeroize;
@@ -118,20 +119,29 @@ fn auth_probe_record_failure_with_state(
     peer_ip: IpAddr,
     now: Instant,
 ) {
-    if let Some(mut entry) = state.get_mut(&peer_ip) {
-        if auth_probe_state_expired(&entry, now) {
-            *entry = AuthProbeState {
-                fail_streak: 1,
-                blocked_until: now + auth_probe_backoff(1),
-                last_seen: now,
-            };
+    let make_new_state = || AuthProbeState {
+        fail_streak: 1,
+        blocked_until: now + auth_probe_backoff(1),
+        last_seen: now,
+    };
+
+    let update_existing = |entry: &mut AuthProbeState| {
+        if auth_probe_state_expired(entry, now) {
+            *entry = make_new_state();
+        } else {
+            entry.fail_streak = entry.fail_streak.saturating_add(1);
+            entry.last_seen = now;
+            entry.blocked_until = now + auth_probe_backoff(entry.fail_streak);
+        }
+    };
+
+    match state.entry(peer_ip) {
+        Entry::Occupied(mut entry) => {
+            update_existing(entry.get_mut());
             return;
         }
-        entry.fail_streak = entry.fail_streak.saturating_add(1);
-        entry.last_seen = now;
-        entry.blocked_until = now + auth_probe_backoff(entry.fail_streak);
-        return;
-    };
+        Entry::Vacant(_) => {}
+    }
 
     if state.len() >= AUTH_PROBE_TRACK_MAX_ENTRIES {
         let mut stale_keys = Vec::new();
@@ -155,11 +165,14 @@ fn auth_probe_record_failure_with_state(
         }
     }
 
-    state.insert(peer_ip, AuthProbeState {
-        fail_streak: 1,
-        blocked_until: now + auth_probe_backoff(1),
-        last_seen: now,
-    });
+    match state.entry(peer_ip) {
+        Entry::Occupied(mut entry) => {
+            update_existing(entry.get_mut());
+        }
+        Entry::Vacant(entry) => {
+            entry.insert(make_new_state());
+        }
+    }
 }
 
 fn auth_probe_record_success(peer_ip: IpAddr) {
diff --git a/src/proxy/handshake_security_tests.rs b/src/proxy/handshake_security_tests.rs
index d8d8d3b..6bdc345 100644
--- a/src/proxy/handshake_security_tests.rs
+++ b/src/proxy/handshake_security_tests.rs
@@ -4,6 +4,7 @@ use dashmap::DashMap;
 use std::net::{IpAddr, Ipv4Addr};
 use std::sync::Arc;
 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;
@@ -994,3 +995,116 @@ fn auth_probe_eviction_offset_varies_with_input() {
     assert_eq!(a, b, "same input must yield deterministic offset");
     assert_ne!(a, c, "different peer IPs should not collapse to one offset");
 }
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 4)]
+async fn auth_probe_concurrent_failures_do_not_lose_fail_streak_updates() {
+    let _guard = auth_probe_test_lock()
+        .lock()
+        .unwrap_or_else(|poisoned| poisoned.into_inner());
+    clear_auth_probe_state_for_testing();
+
+    let peer_ip: IpAddr = "198.51.100.90".parse().unwrap();
+    let tasks = 128usize;
+    let barrier = Arc::new(Barrier::new(tasks));
+    let mut handles = Vec::with_capacity(tasks);
+
+    for _ in 0..tasks {
+        let barrier = barrier.clone();
+        handles.push(tokio::spawn(async move {
+            barrier.wait().await;
+            auth_probe_record_failure(peer_ip, Instant::now());
+        }));
+    }
+
+    for handle in handles {
+        handle
+            .await
+            .expect("concurrent failure recording task must not panic");
+    }
+
+    let streak = auth_probe_fail_streak_for_testing(peer_ip)
+        .expect("tracked peer must exist after concurrent failure burst");
+    assert_eq!(
+        streak as usize,
+        tasks,
+        "concurrent failures for one source must account every attempt"
+    );
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 4)]
+async fn invalid_probe_noise_from_other_ips_does_not_break_valid_tls_handshake() {
+    let _guard = auth_probe_test_lock()
+        .lock()
+        .unwrap_or_else(|poisoned| poisoned.into_inner());
+    clear_auth_probe_state_for_testing();
+
+    let secret = [0x31u8; 16];
+    let config = Arc::new(test_config_with_secret_hex("31313131313131313131313131313131"));
+    let replay_checker = Arc::new(ReplayChecker::new(4096, Duration::from_secs(60)));
+    let rng = Arc::new(SecureRandom::new());
+    let victim_peer: SocketAddr = "198.51.100.91:44391".parse().unwrap();
+    let valid = Arc::new(make_valid_tls_handshake(&secret, 0));
+
+    let mut invalid = vec![0x42u8; tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN + 1 + 32];
+    invalid[tls::TLS_DIGEST_POS + tls::TLS_DIGEST_LEN] = 32;
+    let invalid = Arc::new(invalid);
+
+    let mut noise_tasks = Vec::new();
+    for idx in 0..96u16 {
+        let config = config.clone();
+        let replay_checker = replay_checker.clone();
+        let rng = rng.clone();
+        let invalid = invalid.clone();
+        noise_tasks.push(tokio::spawn(async move {
+            let octet = ((idx % 200) + 1) as u8;
+            let peer = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(203, 0, 113, octet)), 45000 + idx);
+            let result = handle_tls_handshake(
+                &invalid,
+                tokio::io::empty(),
+                tokio::io::sink(),
+                peer,
+                &config,
+                &replay_checker,
+                &rng,
+                None,
+            )
+            .await;
+            assert!(matches!(result, HandshakeResult::BadClient { .. }));
+        }));
+    }
+
+    let victim_config = config.clone();
+    let victim_replay_checker = replay_checker.clone();
+    let victim_rng = rng.clone();
+    let victim_valid = valid.clone();
+    let victim_task = tokio::spawn(async move {
+        handle_tls_handshake(
+            &victim_valid,
+            tokio::io::empty(),
+            tokio::io::sink(),
+            victim_peer,
+            &victim_config,
+            &victim_replay_checker,
+            &victim_rng,
+            None,
+        )
+        .await
+    });
+
+    for task in noise_tasks {
+        task.await.expect("noise task must not panic");
+    }
+
+    let victim_result = victim_task
+        .await
+        .expect("victim handshake task must not panic");
+    assert!(
+        matches!(victim_result, HandshakeResult::Success(_)),
+        "invalid probe noise from other IPs must not block a valid victim handshake"
+    );
+    assert_eq!(
+        auth_probe_fail_streak_for_testing(victim_peer.ip()),
+        None,
+        "successful victim handshake must not retain pre-auth failure streak"
+    );
+}
diff --git a/src/proxy/middle_relay.rs b/src/proxy/middle_relay.rs
index 091094d..1acbdc1 100644
--- a/src/proxy/middle_relay.rs
+++ b/src/proxy/middle_relay.rs
@@ -7,7 +7,6 @@ use std::time::{Duration, Instant};
 #[cfg(test)]
 use std::sync::Mutex;
 
-use bytes::Bytes;
 use dashmap::DashMap;
 use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
 use tokio::sync::{mpsc, oneshot, watch};
@@ -24,11 +23,11 @@ use crate::proxy::route_mode::{
     cutover_stagger_delay,
 };
 use crate::stats::Stats;
-use crate::stream::{BufferPool, CryptoReader, CryptoWriter};
+use crate::stream::{BufferPool, CryptoReader, CryptoWriter, PooledBuffer};
 use crate::transport::middle_proxy::{MePool, MeResponse, proto_flags_for_tag};
 
 enum C2MeCommand {
-    Data { payload: Bytes, flags: u32 },
+    Data { payload: PooledBuffer, flags: u32 },
     Close,
 }
 
@@ -686,7 +685,7 @@ async fn read_client_payload<R>(
     forensics: &RelayForensicsState,
     frame_counter: &mut u64,
     stats: &Stats,
-) -> Result<Option<(Bytes, bool)>>
+) -> Result<Option<(PooledBuffer, bool)>>
 where
     R: AsyncRead + Unpin + Send + 'static,
 {
@@ -807,8 +806,7 @@ where
             payload.truncate(secure_payload_len);
         }
         *frame_counter += 1;
-        let payload_bytes = Bytes::copy_from_slice(&payload[..]);
-        return Ok(Some((payload_bytes, quickack)));
+        return Ok(Some((payload, quickack)));
     }
 }
 
diff --git a/src/proxy/middle_relay_security_tests.rs b/src/proxy/middle_relay_security_tests.rs
index 511a853..a2a6c3e 100644
--- a/src/proxy/middle_relay_security_tests.rs
+++ b/src/proxy/middle_relay_security_tests.rs
@@ -1,7 +1,9 @@
 use super::*;
+use bytes::Bytes;
 use crate::crypto::AesCtr;
+use crate::crypto::SecureRandom;
 use crate::stats::Stats;
-use crate::stream::{BufferPool, CryptoReader};
+use crate::stream::{BufferPool, CryptoReader, CryptoWriter, PooledBuffer};
 use std::net::SocketAddr;
 use std::sync::Arc;
 use std::sync::atomic::AtomicU64;
@@ -9,6 +11,21 @@ use tokio::io::AsyncWriteExt;
 use tokio::io::duplex;
 use tokio::time::{Duration as TokioDuration, timeout};
 
+fn make_pooled_payload(data: &[u8]) -> PooledBuffer {
+    let pool = Arc::new(BufferPool::with_config(data.len().max(1), 4));
+    let mut payload = pool.get();
+    payload.resize(data.len(), 0);
+    payload[..data.len()].copy_from_slice(data);
+    payload
+}
+
+fn make_pooled_payload_from(pool: &Arc<BufferPool>, data: &[u8]) -> PooledBuffer {
+    let mut payload = pool.get();
+    payload.resize(data.len(), 0);
+    payload[..data.len()].copy_from_slice(data);
+    payload
+}
+
 #[test]
 fn should_yield_sender_only_on_budget_with_backlog() {
     assert!(!should_yield_c2me_sender(0, true));
@@ -23,7 +40,7 @@ async fn enqueue_c2me_command_uses_try_send_fast_path() {
     enqueue_c2me_command(
         &tx,
         C2MeCommand::Data {
-            payload: Bytes::from_static(&[1, 2, 3]),
+            payload: make_pooled_payload(&[1, 2, 3]),
             flags: 0,
         },
     )
@@ -47,7 +64,7 @@ async fn enqueue_c2me_command_uses_try_send_fast_path() {
 async fn enqueue_c2me_command_falls_back_to_send_when_queue_is_full() {
     let (tx, mut rx) = mpsc::channel::<C2MeCommand>(1);
     tx.send(C2MeCommand::Data {
-        payload: Bytes::from_static(&[9]),
+        payload: make_pooled_payload(&[9]),
         flags: 9,
     })
     .await
@@ -58,7 +75,7 @@ async fn enqueue_c2me_command_falls_back_to_send_when_queue_is_full() {
         enqueue_c2me_command(
             &tx2,
             C2MeCommand::Data {
-                payload: Bytes::from_static(&[7, 7]),
+                payload: make_pooled_payload(&[7, 7]),
                 flags: 7,
             },
         )
@@ -84,6 +101,74 @@ async fn enqueue_c2me_command_falls_back_to_send_when_queue_is_full() {
     }
 }
 
+#[tokio::test]
+async fn enqueue_c2me_command_closed_channel_recycles_payload() {
+    let pool = Arc::new(BufferPool::with_config(64, 4));
+    let payload = make_pooled_payload_from(&pool, &[1, 2, 3, 4]);
+    let (tx, rx) = mpsc::channel::<C2MeCommand>(1);
+    drop(rx);
+
+    let result = enqueue_c2me_command(
+        &tx,
+        C2MeCommand::Data {
+            payload,
+            flags: 0,
+        },
+    )
+    .await;
+
+    assert!(result.is_err(), "closed queue must fail enqueue");
+    drop(result);
+    assert!(
+        pool.stats().pooled >= 1,
+        "payload must return to pool when enqueue fails on closed channel"
+    );
+}
+
+#[tokio::test]
+async fn enqueue_c2me_command_full_then_closed_recycles_waiting_payload() {
+    let pool = Arc::new(BufferPool::with_config(64, 4));
+    let (tx, rx) = mpsc::channel::<C2MeCommand>(1);
+
+    tx.send(C2MeCommand::Data {
+        payload: make_pooled_payload_from(&pool, &[9]),
+        flags: 1,
+    })
+    .await
+    .unwrap();
+
+    let tx2 = tx.clone();
+    let pool2 = pool.clone();
+    let blocked_send = tokio::spawn(async move {
+        enqueue_c2me_command(
+            &tx2,
+            C2MeCommand::Data {
+                payload: make_pooled_payload_from(&pool2, &[7, 7, 7]),
+                flags: 2,
+            },
+        )
+        .await
+    });
+
+    tokio::time::sleep(TokioDuration::from_millis(10)).await;
+    drop(rx);
+
+    let result = timeout(TokioDuration::from_secs(1), blocked_send)
+        .await
+        .expect("blocked send task must finish")
+        .expect("blocked send task must not panic");
+
+    assert!(
+        result.is_err(),
+        "closing receiver while sender is blocked must fail enqueue"
+    );
+    drop(result);
+    assert!(
+        pool.stats().pooled >= 2,
+        "both queued and blocked payloads must return to pool after channel close"
+    );
+}
+
 #[test]
 fn desync_dedup_cache_is_bounded() {
     let _guard = desync_dedup_test_lock()
@@ -150,6 +235,12 @@ fn make_crypto_reader(reader: tokio::io::DuplexStream) -> CryptoReader<tokio::io
     CryptoReader::new(reader, AesCtr::new(&key, iv))
 }
 
+fn make_crypto_writer(writer: tokio::io::DuplexStream) -> CryptoWriter<tokio::io::DuplexStream> {
+    let key = [0u8; 32];
+    let iv = 0u128;
+    CryptoWriter::new(writer, AesCtr::new(&key, iv), 8 * 1024)
+}
+
 fn encrypt_for_reader(plaintext: &[u8]) -> Vec<u8> {
     let key = [0u8; 32];
     let iv = 0u128;
@@ -476,3 +567,215 @@ async fn read_client_payload_returns_buffer_to_pool_after_emit() {
         "emitted payload buffer must be returned to pool to avoid pool drain"
     );
 }
+
+#[tokio::test]
+async fn read_client_payload_keeps_pool_buffer_checked_out_until_frame_drop() {
+    let _guard = desync_dedup_test_lock()
+        .lock()
+        .expect("middle relay test lock must be available");
+
+    let pool = Arc::new(BufferPool::with_config(64, 2));
+    pool.preallocate(1);
+    assert_eq!(pool.stats().pooled, 1, "one pooled buffer must be available");
+
+    let (reader, mut writer) = duplex(1024);
+    let mut crypto_reader = make_crypto_reader(reader);
+    let stats = Stats::new();
+    let forensics = make_forensics_state();
+    let mut frame_counter = 0;
+
+    let payload = [0x41u8, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48];
+    let mut plaintext = Vec::with_capacity(4 + payload.len());
+    plaintext.extend_from_slice(&(payload.len() as u32).to_le_bytes());
+    plaintext.extend_from_slice(&payload);
+    let encrypted = encrypt_for_reader(&plaintext);
+    writer.write_all(&encrypted).await.unwrap();
+
+    let (frame, quickack) = read_client_payload(
+        &mut crypto_reader,
+        ProtoTag::Intermediate,
+        1024,
+        TokioDuration::from_secs(1),
+        &pool,
+        &forensics,
+        &mut frame_counter,
+        &stats,
+    )
+    .await
+    .expect("payload read must succeed")
+    .expect("frame must be present");
+
+    assert!(!quickack);
+    assert_eq!(frame.as_ref(), &payload);
+    assert_eq!(
+        pool.stats().pooled,
+        0,
+        "buffer must stay checked out while frame payload is alive"
+    );
+
+    drop(frame);
+    assert!(
+        pool.stats().pooled >= 1,
+        "buffer must return to pool only after frame drop"
+    );
+}
+
+#[tokio::test]
+async fn enqueue_c2me_close_unblocks_after_queue_drain() {
+    let (tx, mut rx) = mpsc::channel::<C2MeCommand>(1);
+    tx.send(C2MeCommand::Data {
+        payload: make_pooled_payload(&[0x41]),
+        flags: 0,
+    })
+    .await
+    .unwrap();
+
+    let tx2 = tx.clone();
+    let close_task = tokio::spawn(async move { enqueue_c2me_command(&tx2, C2MeCommand::Close).await });
+
+    tokio::time::sleep(TokioDuration::from_millis(10)).await;
+
+    let first = timeout(TokioDuration::from_millis(100), rx.recv())
+        .await
+        .unwrap()
+        .expect("first queued item must be present");
+    assert!(matches!(first, C2MeCommand::Data { .. }));
+
+    close_task.await.unwrap().expect("close enqueue must succeed after drain");
+
+    let second = timeout(TokioDuration::from_millis(100), rx.recv())
+        .await
+        .unwrap()
+        .expect("close command must follow after queue drain");
+    assert!(matches!(second, C2MeCommand::Close));
+}
+
+#[tokio::test]
+async fn enqueue_c2me_close_full_then_receiver_drop_fails_cleanly() {
+    let (tx, rx) = mpsc::channel::<C2MeCommand>(1);
+    tx.send(C2MeCommand::Data {
+        payload: make_pooled_payload(&[0x42]),
+        flags: 0,
+    })
+    .await
+    .unwrap();
+
+    let tx2 = tx.clone();
+    let close_task = tokio::spawn(async move { enqueue_c2me_command(&tx2, C2MeCommand::Close).await });
+
+    tokio::time::sleep(TokioDuration::from_millis(10)).await;
+    drop(rx);
+
+    let result = timeout(TokioDuration::from_secs(1), close_task)
+        .await
+        .expect("close task must finish")
+        .expect("close task must not panic");
+    assert!(
+        result.is_err(),
+        "close enqueue must fail cleanly when receiver is dropped under pressure"
+    );
+}
+
+#[tokio::test]
+async fn process_me_writer_response_ack_obeys_flush_policy() {
+    let (writer_side, _reader_side) = duplex(1024);
+    let mut writer = make_crypto_writer(writer_side);
+    let rng = SecureRandom::new();
+    let mut frame_buf = Vec::new();
+    let stats = Stats::new();
+    let bytes_me2c = AtomicU64::new(0);
+
+    let immediate = process_me_writer_response(
+        MeResponse::Ack(0x11223344),
+        &mut writer,
+        ProtoTag::Intermediate,
+        &rng,
+        &mut frame_buf,
+        &stats,
+        "user",
+        &bytes_me2c,
+        77,
+        true,
+        false,
+    )
+    .await
+    .expect("ack response must be processed");
+
+    assert!(matches!(
+        immediate,
+        MeWriterResponseOutcome::Continue {
+            frames: 1,
+            bytes: 4,
+            flush_immediately: true,
+        }
+    ));
+
+    let delayed = process_me_writer_response(
+        MeResponse::Ack(0x55667788),
+        &mut writer,
+        ProtoTag::Intermediate,
+        &rng,
+        &mut frame_buf,
+        &stats,
+        "user",
+        &bytes_me2c,
+        77,
+        false,
+        false,
+    )
+    .await
+    .expect("ack response must be processed");
+
+    assert!(matches!(
+        delayed,
+        MeWriterResponseOutcome::Continue {
+            frames: 1,
+            bytes: 4,
+            flush_immediately: false,
+        }
+    ));
+}
+
+#[tokio::test]
+async fn process_me_writer_response_data_updates_byte_accounting() {
+    let (writer_side, _reader_side) = duplex(1024);
+    let mut writer = make_crypto_writer(writer_side);
+    let rng = SecureRandom::new();
+    let mut frame_buf = Vec::new();
+    let stats = Stats::new();
+    let bytes_me2c = AtomicU64::new(0);
+
+    let payload = vec![1u8, 2, 3, 4, 5, 6, 7, 8, 9];
+    let outcome = process_me_writer_response(
+        MeResponse::Data {
+            flags: 0,
+            data: Bytes::from(payload.clone()),
+        },
+        &mut writer,
+        ProtoTag::Intermediate,
+        &rng,
+        &mut frame_buf,
+        &stats,
+        "user",
+        &bytes_me2c,
+        88,
+        false,
+        false,
+    )
+    .await
+    .expect("data response must be processed");
+
+    assert!(matches!(
+        outcome,
+        MeWriterResponseOutcome::Continue {
+            frames: 1,
+            bytes,
+            flush_immediately: false,
+        } if bytes == payload.len()
+    ));
+    assert_eq!(
+        bytes_me2c.load(std::sync::atomic::Ordering::Relaxed),
+        payload.len() as u64,
+        "ME->C byte accounting must increase by emitted payload size"
+    );
+}