fix(ws): preserve Codex continuation bindings

apps/aether-gateway/src/handlers/proxy/websocket/responses/binding.rs

@@ -70,6 +70,7 @@ impl UpstreamBindingIdentity {
             .map_err(|_| UpstreamBindingIdentityError::InvalidUpstreamUrl)?
             .to_string();
 
+        let adapter_kind = adapter.kind();
         let headers = websocket_handshake_headers(&decision.provider_request_headers, "invalid")
             .map_err(|_| UpstreamBindingIdentityError::InvalidHandshakeHeaders)?;
         let authentication_header_names = authentication_header_names(decision);
@@ -82,7 +83,7 @@ impl UpstreamBindingIdentity {
                 .map_err(|_| UpstreamBindingIdentityError::InvalidHandshakeHeaders)?;
             if authentication_header_names.contains(name.as_str()) {
                 authentication_headers.insert(name, value.to_string());
-            } else {
+            } else if !is_turn_scoped_handshake_header(adapter_kind, name.as_str()) {
                 handshake_headers.insert(name, value.to_string());
             }
         }
@@ -90,7 +91,7 @@ impl UpstreamBindingIdentity {
             credential_binding_fingerprint(decision, &authentication_headers);
 
         Ok(Self {
-            adapter_kind: adapter.kind(),
+            adapter_kind,
             provider_id: decision.provider_id.clone(),
             endpoint_id: decision.endpoint_id.clone(),
             key_id: decision.key_id.clone(),
@@ -101,6 +102,58 @@ impl UpstreamBindingIdentity {
             transport_profile: decision.transport_profile.clone(),
         })
     }
+
+    /// Returns only safe field/header names for operator diagnostics. Header
+    /// values and credential fingerprints must never reach logs.
+    pub(super) fn changed_field_names(&self, other: &Self) -> Vec<String> {
+        let mut changed = Vec::new();
+        if self.adapter_kind != other.adapter_kind {
+            changed.push("adapter_kind".to_string());
+        }
+        if self.provider_id != other.provider_id {
+            changed.push("provider_id".to_string());
+        }
+        if self.endpoint_id != other.endpoint_id {
+            changed.push("endpoint_id".to_string());
+        }
+        if self.key_id != other.key_id {
+            changed.push("key_id".to_string());
+        }
+        if self.upstream_url != other.upstream_url {
+            changed.push("upstream_url".to_string());
+        }
+        for name in self
+            .handshake_headers
+            .keys()
+            .chain(other.handshake_headers.keys())
+            .collect::<BTreeSet<_>>()
+        {
+            if self.handshake_headers.get(name) != other.handshake_headers.get(name) {
+                changed.push(format!("handshake_header:{name}"));
+            }
+        }
+        if self.credential_fingerprint != other.credential_fingerprint {
+            changed.push("credential_fingerprint".to_string());
+        }
+        if self.proxy != other.proxy {
+            changed.push("proxy".to_string());
+        }
+        if self.transport_profile != other.transport_profile {
+            changed.push("transport_profile".to_string());
+        }
+        changed
+    }
+}
+
+/// `x-codex-turn-metadata` describes one logical response turn. Fingerprint
+/// convergence intentionally rewrites its `turn_id` and timestamp for every
+/// `response.create`, including a continuation on an already-upgraded socket.
+/// It therefore cannot identify the physical handshake that owns a
+/// `previous_response_id`; the per-turn copy in `client_metadata` still travels
+/// in the response.create body.
+fn is_turn_scoped_handshake_header(adapter_kind: ResponsesWebSocketAdapter, name: &str) -> bool {
+    adapter_kind == ResponsesWebSocketAdapter::Codex
+        && name.eq_ignore_ascii_case("x-codex-turn-metadata")
 }
 
 /// Header names that carry credentials in the provider handshake.  The
@@ -434,6 +487,81 @@ mod tests {
         );
     }
 
+    #[test]
+    fn codex_turn_metadata_changes_do_not_change_the_physical_binding() {
+        let adapter = resolve_responses_websocket_adapter(ResponsesWebSocketAdapter::Codex);
+        let mut first = decision();
+        first.provider_type = Some("codex".to_string());
+        first.report_context = Some(json!({
+            "codex_credential_generation": "credential-generation-1"
+        }));
+        first.provider_request_headers.insert(
+            "x-codex-turn-metadata".to_string(),
+            json!({
+                "session_id": "session-1",
+                "thread_id": "thread-1",
+                "turn_id": "turn-1",
+                "turn_started_at_unix_ms": 1
+            })
+            .to_string(),
+        );
+        let first_identity = UpstreamBindingIdentity::from_decision(adapter, &first).unwrap();
+        assert!(!first_identity
+            .handshake_headers
+            .contains_key("x-codex-turn-metadata"));
+
+        let mut continuation = first;
+        continuation.provider_request_headers.insert(
+            "x-codex-turn-metadata".to_string(),
+            json!({
+                "session_id": "session-1",
+                "thread_id": "thread-1",
+                "turn_id": "turn-2",
+                "turn_started_at_unix_ms": 2
+            })
+            .to_string(),
+        );
+        assert_eq!(
+            first_identity,
+            UpstreamBindingIdentity::from_decision(adapter, &continuation).unwrap()
+        );
+    }
+
+    #[test]
+    fn only_codex_turn_metadata_is_excluded_from_binding_headers() {
+        let codex_adapter = resolve_responses_websocket_adapter(ResponsesWebSocketAdapter::Codex);
+        let mut first = decision();
+        first.provider_type = Some("codex".to_string());
+        first.report_context = Some(json!({
+            "codex_credential_generation": "credential-generation-1"
+        }));
+        first.provider_request_headers.insert(
+            "x-codex-turn-metadata".to_string(),
+            r#"{"turn_id":"turn-1"}"#.to_string(),
+        );
+        let first_identity = UpstreamBindingIdentity::from_decision(codex_adapter, &first).unwrap();
+
+        let mut changed = first;
+        changed
+            .provider_request_headers
+            .insert("x-codex-window-id".to_string(), "window-2".to_string());
+        let changed_identity =
+            UpstreamBindingIdentity::from_decision(codex_adapter, &changed).unwrap();
+        assert_ne!(first_identity, changed_identity);
+        assert_eq!(
+            first_identity.changed_field_names(&changed_identity),
+            vec!["handshake_header:x-codex-window-id".to_string()]
+        );
+
+        let standard_adapter =
+            resolve_responses_websocket_adapter(ResponsesWebSocketAdapter::Standard);
+        let standard_identity =
+            UpstreamBindingIdentity::from_decision(standard_adapter, &changed).unwrap();
+        assert!(standard_identity
+            .handshake_headers
+            .contains_key("x-codex-turn-metadata"));
+    }
+
     #[test]
     fn codex_authorization_override_changes_binding_with_the_same_generation() {
         let adapter = resolve_responses_websocket_adapter(ResponsesWebSocketAdapter::Codex);

apps/aether-gateway/src/handlers/proxy/websocket/responses/client.rs

@@ -29,7 +29,9 @@ use super::turn::{
     ResponsesWebSocketTurnOutcome,
 };
 use super::turn_state::LogicalTurn;
-use super::upstream::{bind_responses_upstream, decision_reuses_bound_upstream};
+use super::upstream::{
+    bind_responses_upstream, decision_bound_upstream_change_fields, decision_reuses_bound_upstream,
+};
 use crate::ai_serving::ResponsesWebSocketPinnedCandidate;
 use crate::clock::current_unix_secs;
 use crate::control::GatewayControlDecision;
@@ -496,9 +498,15 @@ async fn forward_pinned_continuation(
     let normalization = planned.normalization;
     let decision = planned.execution;
     let planned_provider_model = provider_model_from_decision(&decision);
-    if !decision_reuses_bound_upstream(bound, adapter, &decision)
-        || planned_provider_model.as_deref() != Some(bound.provider_model.as_str())
-    {
+    let reuses_bound_upstream = decision_reuses_bound_upstream(bound, adapter, &decision);
+    let provider_model_changed =
+        planned_provider_model.as_deref() != Some(bound.provider_model.as_str());
+    if !reuses_bound_upstream || provider_model_changed {
+        let binding_change_fields = if reuses_bound_upstream {
+            Vec::new()
+        } else {
+            decision_bound_upstream_change_fields(bound, adapter, &decision)
+        };
         planned_lease.release().await;
         warn!(
             event_name = "responses_websocket_continuation_binding_changed",
@@ -507,6 +515,8 @@ async fn forward_pinned_continuation(
             websocket = true,
             trace_id = %context.trace_id,
             key_id = ?decision.key_id,
+            binding_change_fields = ?binding_change_fields,
+            provider_model_changed,
             "gateway rejected a continuation after the pinned candidate's physical binding changed"
         );
         send_gateway_error_with_status(

apps/aether-gateway/src/handlers/proxy/websocket/responses/session.rs

@@ -64,7 +64,7 @@ macro_rules! warn {
     };
 }
 
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
 enum InitialMessageError {
     TimedOut,
     ClientClosed,
@@ -76,6 +76,69 @@ enum InitialMessageError {
     InvalidModel,
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+struct InitialMessageFrameMetadata {
+    opcode: &'static str,
+    bytes: usize,
+}
+
+impl InitialMessageFrameMetadata {
+    fn from_message(message: &AxumWsMessage) -> Self {
+        match message {
+            AxumWsMessage::Text(text) => Self {
+                opcode: "text",
+                bytes: text.len(),
+            },
+            AxumWsMessage::Binary(payload) => Self {
+                opcode: "binary",
+                bytes: payload.len(),
+            },
+            AxumWsMessage::Ping(payload) => Self {
+                opcode: "ping",
+                bytes: payload.len(),
+            },
+            AxumWsMessage::Pong(payload) => Self {
+                opcode: "pong",
+                bytes: payload.len(),
+            },
+            AxumWsMessage::Close(frame) => Self {
+                opcode: "close",
+                // Only the payload length is retained. The untrusted close
+                // reason itself must never cross the logging boundary.
+                bytes: frame
+                    .as_ref()
+                    .map_or(0, |frame| 2usize.saturating_add(frame.reason.len())),
+            },
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+struct InitialMessageFailure {
+    error: InitialMessageError,
+    last_frame: Option<InitialMessageFrameMetadata>,
+}
+
+impl InitialMessageFailure {
+    const fn new(
+        error: InitialMessageError,
+        last_frame: Option<InitialMessageFrameMetadata>,
+    ) -> Self {
+        Self { error, last_frame }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+struct InitialMessageDiagnostic {
+    error_code: &'static str,
+    error_kind: &'static str,
+    client_message: Option<&'static str>,
+    close_code: u16,
+    timed_out: bool,
+    last_frame_opcode: Option<&'static str>,
+    last_frame_bytes: Option<usize>,
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 enum ConnectionTermination {
     ConnectionLimitReached,
@@ -106,6 +169,100 @@ impl InitialMessageError {
             }
         }
     }
+
+    const fn client_message(self) -> Option<&'static str> {
+        match self {
+            Self::TimedOut => Some("Timed out waiting for the initial response.create event"),
+            Self::ClientClosed => None,
+            Self::ClientRead => {
+                Some("Failed to read the initial WebSocket event before response.create")
+            }
+            Self::UnsupportedFrame => {
+                Some("The initial response.create event must be sent as a text WebSocket message")
+            }
+            Self::InvalidJson => {
+                Some("The initial WebSocket text message must be a JSON response.create object")
+            }
+            Self::MissingResponseCreate => {
+                Some("The initial WebSocket JSON object must have type response.create")
+            }
+            Self::MissingModel => Some("The initial response.create event must include a model"),
+            Self::InvalidModel => {
+                Some("response.create.model must be a non-empty string no longer than 256 bytes")
+            }
+        }
+    }
+
+    const fn kind(self) -> &'static str {
+        match self {
+            Self::TimedOut => "timeout",
+            Self::ClientClosed => "client_closed",
+            Self::ClientRead => "client_read_failed",
+            Self::UnsupportedFrame => "unsupported_frame",
+            Self::InvalidJson => "invalid_json",
+            Self::MissingResponseCreate => "unexpected_event_type",
+            Self::MissingModel => "missing_model",
+            Self::InvalidModel => "invalid_model",
+        }
+    }
+
+    const fn timed_out(self) -> bool {
+        matches!(self, Self::TimedOut)
+    }
+}
+
+fn initial_message_diagnostic(failure: InitialMessageFailure) -> InitialMessageDiagnostic {
+    InitialMessageDiagnostic {
+        error_code: failure.error.code(),
+        error_kind: failure.error.kind(),
+        client_message: failure.error.client_message(),
+        close_code: failure.error.close_code(),
+        timed_out: failure.error.timed_out(),
+        last_frame_opcode: failure.last_frame.map(|frame| frame.opcode),
+        last_frame_bytes: failure.last_frame.map(|frame| frame.bytes),
+    }
+}
+
+fn log_initial_message_failure(
+    context: &WebSocketRequestContext,
+    failure: InitialMessageFailure,
+    upgraded_at: std::time::Instant,
+) {
+    let diagnostic = initial_message_diagnostic(failure);
+    let auth_context = context.decision.auth_context.as_ref();
+
+    // Initial-frame validation intentionally runs before provider planning, so
+    // no provider identity exists yet. Keep the usual identity fields in the
+    // event schema and say so explicitly instead of guessing from request data.
+    warn!(
+        event_name = "responses_websocket_initial_event_rejected",
+        log_type = "ops",
+        transport = WEBSOCKET_LOG_TRANSPORT,
+        websocket = true,
+        trace_id = %context.trace_id,
+        user_id = auth_context.map(|auth| auth.user_id.as_str()).unwrap_or("-"),
+        api_key_id = auth_context
+            .map(|auth| auth.api_key_id.as_str())
+            .unwrap_or("-"),
+        provider_selected = false,
+        provider_id = "<unplanned>",
+        endpoint_id = "<unplanned>",
+        key_id = "<unplanned>",
+        path = %context.uri.path(),
+        route_class = context.decision.route_class.as_deref().unwrap_or("-"),
+        route_kind = context.decision.route_kind.as_deref().unwrap_or("-"),
+        error_code = diagnostic.error_code,
+        error_kind = diagnostic.error_kind,
+        close_code = diagnostic.close_code,
+        timed_out = diagnostic.timed_out,
+        upgrade_to_initial_outcome_ms = upgraded_at.elapsed().as_millis() as u64,
+        initial_message_timeout_ms = RESPONSES_WEBSOCKET_SESSION_LIMITS
+            .initial_message_timeout
+            .as_millis() as u64,
+        last_frame_opcode = diagnostic.last_frame_opcode.unwrap_or("none"),
+        last_frame_bytes = ?diagnostic.last_frame_bytes,
+        "gateway rejected the initial Responses WebSocket event"
+    );
 }
 
 pub(super) async fn run_responses_websocket(
@@ -113,6 +270,7 @@ pub(super) async fn run_responses_websocket(
     state: AppState,
     mut context: WebSocketRequestContext,
 ) {
+    let upgraded_at = std::time::Instant::now();
     // The public connection limit starts when the HTTP Upgrade hands us the
     // socket, not after provider planning and its upstream handshake finish.
     let connection_deadline =
@@ -122,7 +280,7 @@ pub(super) async fn run_responses_websocket(
     connection_log.log_opened();
 
     let bootstrap_result = supervise_responses_websocket_phase(
-        bootstrap_responses_websocket(&mut client_socket, state.clone(), &context),
+        bootstrap_responses_websocket(&mut client_socket, state.clone(), &context, upgraded_at),
         connection_deadline,
         connection_permit.as_ref(),
     )
@@ -196,19 +354,20 @@ async fn bootstrap_responses_websocket(
     client_socket: &mut WebSocket,
     state: AppState,
     context: &WebSocketRequestContext,
+    upgraded_at: std::time::Instant,
 ) -> Option<BoundResponsesConnection> {
     let (_first_text, first_event) = match receive_initial_response_create(client_socket).await {
         Ok(value) => value,
-        Err(error) => {
-            if !matches!(error, InitialMessageError::ClientClosed) {
-                send_gateway_error(
+        Err(failure) => {
+            if let Some(client_message) = failure.error.client_message() {
+                log_initial_message_failure(context, failure, upgraded_at);
+                send_gateway_error(client_socket, failure.error.code(), client_message).await;
+                close_client_socket(
                     client_socket,
-                    error.code(),
-                    "WebSocket must start with a valid response.create event",
+                    failure.error.close_code(),
+                    "invalid_initial_event",
                 )
                 .await;
-                close_client_socket(client_socket, error.close_code(), "invalid_initial_event")
-                    .await;
             }
             return None;
         }
@@ -598,7 +757,7 @@ async fn close_terminated_relay(
 /// 但不会重置计时器。防止客户端通过周期性 Ping 无限占用 connection permit。
 async fn receive_initial_response_create(
     client_socket: &mut WebSocket,
-) -> Result<(String, Value), InitialMessageError> {
+) -> Result<(String, Value), InitialMessageFailure> {
     receive_initial_response_create_with_deadline(
         client_socket,
         RESPONSES_WEBSOCKET_SESSION_LIMITS.initial_message_timeout,
@@ -615,7 +774,7 @@ async fn receive_initial_response_create(
 async fn receive_initial_response_create_with_deadline<S>(
     socket: &mut S,
     deadline_budget: std::time::Duration,
-) -> Result<(String, Value), InitialMessageError>
+) -> Result<(String, Value), InitialMessageFailure>
 where
     S: futures_util::Stream<Item = Result<AxumWsMessage, axum::Error>>
         + futures_util::Sink<AxumWsMessage, Error = axum::Error>
@@ -625,29 +784,51 @@ where
 
     // 绝对 deadline：入口计算一次，后续所有迭代共享，Ping/Pong 不会重启
     let deadline = tokio::time::Instant::now() + deadline_budget;
+    let mut last_frame = None;
     loop {
         let message = tokio::time::timeout_at(deadline, socket.next())
             .await
-            .map_err(|_| InitialMessageError::TimedOut)?;
+            .map_err(|_| InitialMessageFailure::new(InitialMessageError::TimedOut, last_frame))?;
         let Some(message) = message else {
-            return Err(InitialMessageError::ClientClosed);
+            return Err(InitialMessageFailure::new(
+                InitialMessageError::ClientClosed,
+                last_frame,
+            ));
         };
-        let message = message.map_err(|_| InitialMessageError::ClientRead)?;
+        let message = message
+            .map_err(|_| InitialMessageFailure::new(InitialMessageError::ClientRead, last_frame))?;
+        last_frame = Some(InitialMessageFrameMetadata::from_message(&message));
         match message {
             AxumWsMessage::Ping(payload) => {
                 tokio::time::timeout_at(deadline, socket.send(AxumWsMessage::Pong(payload)))
                     .await
-                    .map_err(|_| InitialMessageError::TimedOut)?
-                    .map_err(|_| InitialMessageError::ClientRead)?;
+                    .map_err(|_| {
+                        InitialMessageFailure::new(InitialMessageError::TimedOut, last_frame)
+                    })?
+                    .map_err(|_| {
+                        InitialMessageFailure::new(InitialMessageError::ClientRead, last_frame)
+                    })?;
             }
             AxumWsMessage::Pong(_) => {}
-            AxumWsMessage::Close(_) => return Err(InitialMessageError::ClientClosed),
-            AxumWsMessage::Binary(_) => return Err(InitialMessageError::UnsupportedFrame),
+            AxumWsMessage::Close(_) => {
+                return Err(InitialMessageFailure::new(
+                    InitialMessageError::ClientClosed,
+                    last_frame,
+                ));
+            }
+            AxumWsMessage::Binary(_) => {
+                return Err(InitialMessageFailure::new(
+                    InitialMessageError::UnsupportedFrame,
+                    last_frame,
+                ));
+            }
             AxumWsMessage::Text(text) => {
                 let text = text.to_string();
-                let event: Value =
-                    serde_json::from_str(&text).map_err(|_| InitialMessageError::InvalidJson)?;
-                validate_initial_response_create(&event)?;
+                let event: Value = serde_json::from_str(&text).map_err(|_| {
+                    InitialMessageFailure::new(InitialMessageError::InvalidJson, last_frame)
+                })?;
+                validate_initial_response_create(&event)
+                    .map_err(|error| InitialMessageFailure::new(error, last_frame))?;
                 return Ok((text, event));
             }
         }
@@ -737,6 +918,109 @@ mod tests {
         }
     }
 
+    #[test]
+    fn initial_message_error_diagnostics_are_stable() {
+        use super::{initial_message_diagnostic, InitialMessageError, InitialMessageFailure};
+
+        let cases = [
+            (
+                InitialMessageError::TimedOut,
+                "initial_response_create_timeout",
+                "timeout",
+                Some("Timed out waiting for the initial response.create event"),
+                1013,
+                true,
+            ),
+            (
+                InitialMessageError::ClientClosed,
+                "client_closed",
+                "client_closed",
+                None,
+                1000,
+                false,
+            ),
+            (
+                InitialMessageError::ClientRead,
+                "client_read_failed",
+                "client_read_failed",
+                Some("Failed to read the initial WebSocket event before response.create"),
+                1008,
+                false,
+            ),
+            (
+                InitialMessageError::UnsupportedFrame,
+                "initial_response_create_must_be_text",
+                "unsupported_frame",
+                Some("The initial response.create event must be sent as a text WebSocket message"),
+                1008,
+                false,
+            ),
+            (
+                InitialMessageError::InvalidJson,
+                "invalid_response_create",
+                "invalid_json",
+                Some("The initial WebSocket text message must be a JSON response.create object"),
+                1008,
+                false,
+            ),
+            (
+                InitialMessageError::MissingResponseCreate,
+                "expected_response_create",
+                "unexpected_event_type",
+                Some("The initial WebSocket JSON object must have type response.create"),
+                1008,
+                false,
+            ),
+            (
+                InitialMessageError::MissingModel,
+                "response_create_model_required",
+                "missing_model",
+                Some("The initial response.create event must include a model"),
+                1008,
+                false,
+            ),
+            (
+                InitialMessageError::InvalidModel,
+                "invalid_response_create_model",
+                "invalid_model",
+                Some("response.create.model must be a non-empty string no longer than 256 bytes"),
+                1008,
+                false,
+            ),
+        ];
+
+        for (error, error_code, error_kind, client_message, close_code, timed_out) in cases {
+            let diagnostic = initial_message_diagnostic(InitialMessageFailure::new(error, None));
+            assert_eq!(diagnostic.error_code, error_code);
+            assert_eq!(diagnostic.error_kind, error_kind);
+            assert_eq!(diagnostic.client_message, client_message);
+            assert_eq!(diagnostic.close_code, close_code);
+            assert_eq!(diagnostic.timed_out, timed_out);
+            assert_eq!(diagnostic.last_frame_opcode, None);
+            assert_eq!(diagnostic.last_frame_bytes, None);
+        }
+    }
+
+    #[test]
+    fn initial_message_diagnostic_retains_only_safe_frame_shape() {
+        use super::{
+            initial_message_diagnostic, InitialMessageError, InitialMessageFailure,
+            InitialMessageFrameMetadata,
+        };
+
+        let secret_body = r#"{"type":"not-response.create","token":"must-not-log"}"#;
+        let frame = Message::Text(secret_body.to_string().into());
+        let metadata = InitialMessageFrameMetadata::from_message(&frame);
+        let diagnostic = initial_message_diagnostic(InitialMessageFailure::new(
+            InitialMessageError::MissingResponseCreate,
+            Some(metadata),
+        ));
+
+        assert_eq!(diagnostic.last_frame_opcode, Some("text"));
+        assert_eq!(diagnostic.last_frame_bytes, Some(secret_body.len()));
+        assert!(!format!("{diagnostic:?}").contains("must-not-log"));
+    }
+
     #[tokio::test]
     async fn phase_supervisor_drops_work_at_the_absolute_connection_deadline() {
         let dropped = Arc::new(AtomicUsize::new(0));
@@ -1535,7 +1819,10 @@ mod tests {
         .await
         .expect("the initial-message deadline must cancel a stalled Pong write");
 
-        assert!(matches!(result, Err(InitialMessageError::TimedOut)));
+        assert!(matches!(
+            &result,
+            Err(failure) if failure.error == InitialMessageError::TimedOut
+        ));
     }
 
     /// 验证 receive_initial_response_create_with_deadline 的绝对 deadline：
@@ -1583,7 +1870,10 @@ mod tests {
         ping_task.abort();
 
         assert!(
-            matches!(result, Err(InitialMessageError::TimedOut)),
+            matches!(
+                &result,
+                Err(failure) if failure.error == InitialMessageError::TimedOut
+            ),
             "expected TimedOut after absolute deadline, got: {result:?}"
         );
     }

apps/aether-gateway/src/handlers/proxy/websocket/responses/upstream.rs

@@ -156,6 +156,20 @@ pub(super) fn decision_reuses_bound_upstream(
             .unwrap_or(false)
 }
 
+pub(super) fn decision_bound_upstream_change_fields(
+    bound: &BoundResponsesConnection,
+    adapter: &'static dyn ResponsesWebSocketProtocolAdapter,
+    decision: &AiExecutionDecision,
+) -> Vec<String> {
+    if bound.upstream.is_none() {
+        return vec!["upstream_socket".to_string()];
+    }
+    match UpstreamBindingIdentity::from_decision(adapter, decision) {
+        Ok(identity) => bound.binding_identity.changed_field_names(&identity),
+        Err(_) => vec!["binding_identity_invalid".to_string()],
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use std::time::Duration;