Apply [timeouts] tg_connect to upstream DC TCP connect attempts

Wire config.timeouts.tg_connect into UpstreamManager; per-attempt timeout uses
the same .max(1) pattern as connect_budget_ms.

Reject timeouts.tg_connect = 0 at config load (consistent with
general.upstream_connect_budget_ms and related checks). Default when the key
is omitted remains default_connect_timeout() via serde.

Fixes telemt/telemt#439

src/config/load.rs

@@ -346,6 +346,12 @@ impl ProxyConfig {
             ));
         }
 
+        if config.timeouts.tg_connect == 0 {
+            return Err(ProxyError::Config(
+                "timeouts.tg_connect must be > 0".to_string(),
+            ));
+        }
+
         if config.general.upstream_unhealthy_fail_threshold == 0 {
             return Err(ProxyError::Config(
                 "general.upstream_unhealthy_fail_threshold must be > 0".to_string(),
@@ -1625,6 +1631,26 @@ mod tests {
         let _ = std::fs::remove_file(path);
     }
 
+    #[test]
+    fn tg_connect_zero_is_rejected() {
+        let toml = r#"
+            [timeouts]
+            tg_connect = 0
+
+            [censorship]
+            tls_domain = "example.com"
+
+            [access.users]
+            user = "00000000000000000000000000000000"
+        "#;
+        let dir = std::env::temp_dir();
+        let path = dir.join("telemt_tg_connect_zero_test.toml");
+        std::fs::write(&path, toml).unwrap();
+        let err = ProxyConfig::load(&path).unwrap_err().to_string();
+        assert!(err.contains("timeouts.tg_connect must be > 0"));
+        let _ = std::fs::remove_file(path);
+    }
+
     #[test]
     fn rpc_proxy_req_every_out_of_range_is_rejected() {
         let toml = r#"

src/maestro/mod.rs

@@ -191,6 +191,7 @@ pub async fn run() -> std::result::Result<(), Box<dyn std::error::Error>> {
         config.general.upstream_connect_retry_attempts,
         config.general.upstream_connect_retry_backoff_ms,
         config.general.upstream_connect_budget_ms,
+        config.timeouts.tg_connect,
         config.general.upstream_unhealthy_fail_threshold,
         config.general.upstream_connect_failfast_hard_errors,
         stats.clone(),

src/transport/upstream.rs

@@ -34,8 +34,6 @@ const NUM_DCS: usize = 5;
 
 /// Timeout for individual DC ping attempt
 const DC_PING_TIMEOUT_SECS: u64 = 5;
-/// Timeout for direct TG DC TCP connect readiness.
-const DIRECT_CONNECT_TIMEOUT_SECS: u64 = 10;
 /// Interval between upstream health-check cycles.
 const HEALTH_CHECK_INTERVAL_SECS: u64 = 30;
 /// Timeout for a single health-check connect attempt.
@@ -319,6 +317,8 @@ pub struct UpstreamManager {
     connect_retry_attempts: u32,
     connect_retry_backoff: Duration,
     connect_budget: Duration,
+    /// Per-attempt TCP connect timeout to Telegram DC (`[timeouts] tg_connect`, seconds).
+    tg_connect_timeout_secs: u64,
     unhealthy_fail_threshold: u32,
     connect_failfast_hard_errors: bool,
     no_upstreams_warn_epoch_ms: Arc<AtomicU64>,
@@ -332,6 +332,7 @@ impl UpstreamManager {
         connect_retry_attempts: u32,
         connect_retry_backoff_ms: u64,
         connect_budget_ms: u64,
+        tg_connect_timeout_secs: u64,
         unhealthy_fail_threshold: u32,
         connect_failfast_hard_errors: bool,
         stats: Arc<Stats>,
@@ -347,6 +348,7 @@ impl UpstreamManager {
             connect_retry_attempts: connect_retry_attempts.max(1),
             connect_retry_backoff: Duration::from_millis(connect_retry_backoff_ms),
             connect_budget: Duration::from_millis(connect_budget_ms.max(1)),
+            tg_connect_timeout_secs: tg_connect_timeout_secs.max(1),
             unhealthy_fail_threshold: unhealthy_fail_threshold.max(1),
             connect_failfast_hard_errors,
             no_upstreams_warn_epoch_ms: Arc::new(AtomicU64::new(0)),
@@ -797,8 +799,8 @@ impl UpstreamManager {
                 break;
             }
             let remaining_budget = self.connect_budget.saturating_sub(elapsed);
-            let attempt_timeout =
-                Duration::from_secs(DIRECT_CONNECT_TIMEOUT_SECS).min(remaining_budget);
+            let attempt_timeout = Duration::from_secs(self.tg_connect_timeout_secs)
+                .min(remaining_budget);
             if attempt_timeout.is_zero() {
                 last_error = Some(ProxyError::ConnectionTimeout {
                     addr: target.to_string(),
@@ -1901,6 +1903,7 @@ mod tests {
             1,
             100,
             1000,
+            10,
             1,
             false,
             Arc::new(Stats::new()),