fix(stream): message-in-chat check and don't stack resume requests

- Added message-in-chat binding check alongside the existing chat-
  ownership check. Both use the same already-fetched chat object, so
  this is still one DB round-trip. Defense-in-depth for the case
  where a client supplies one of its own chat_ids but a different
  chat's message_id — the user-scoped key would still serve the
  request otherwise.

- requestResumeForMessage now early-returns if a fence already
  exists for the same message. Fixes two operational concerns:
    * Mixed-version deployments where an older backend doesn't echo
      request_id: previously every reconnect reset the fence timer
      AND set a new request_id, so no reply could ever match; now
      the first fence runs to completion or timeout and only
      subsequent requests after that get a fresh chance.
    * Rapid reconnect churn: used to kick the timer forward
      indefinitely, now one fence per message lifecycle.

backend/open_webui/socket/main.py

@@ -759,21 +759,30 @@ async def resume_stream(sid, data):
             last_seq = int(data.get('last_seq') or 0)
         except (TypeError, ValueError):
             last_seq = 0
-        # Defense-in-depth: validate chat ownership even though the log
-        # key is already user-scoped. Fails CLOSED on DB errors so an
-        # infra hiccup can't skip the ownership check. When chat_id is
-        # absent we fall through to the user-scoped key guarantee so
-        # legacy clients that don't send chat_id still work. Either way
-        # we reply with (at worst) empty envelopes below so the client
-        # fence clears deterministically.
+        # Defense-in-depth: validate chat ownership AND message-in-chat
+        # binding even though the log key is already user-scoped. Fails
+        # CLOSED on DB errors so an infra hiccup can't skip the check.
+        # When chat_id is absent we fall through to the user-scoped key
+        # guarantee so legacy clients that don't send chat_id still work.
+        # Either way we reply with (at worst) empty envelopes below so
+        # the client fence clears deterministically.
         chat_id = data.get('chat_id')
         chat_ok = True
         if chat_id:
             try:
                 chat = await Chats.get_chat_by_id_and_user_id(chat_id, user_id)
-                chat_ok = chat is not None
+                if not chat:
+                    chat_ok = False
+                else:
+                    # Reuse the chat record for the message-in-chat check
+                    # so we don't pay a second DB round-trip.
+                    messages = (
+                        getattr(chat, 'chat', {}) or {}
+                    ).get('history', {}).get('messages', {}) or {}
+                    if message_id not in messages:
+                        chat_ok = False
             except Exception as e:
-                log.warning(f'resume-stream chat ownership check failed: {e}')
+                log.warning(f'resume-stream chat/message check failed: {e}')
                 chat_ok = False
         if chat_ok:
             envelopes = await _stream_log_read(user_id, message_id, last_seq)

src/lib/components/chat/Chat.svelte

@@ -687,10 +687,14 @@
 	const requestResumeForMessage = (message) => {
 		if (!message || !message.id || message.done) return;
 		if (!$socket || !$socket.connected) return;
-		// Fence up before emit so racing live frames get buffered.
-		if (!resumeQueueByMessageId.has(message.id)) {
-			resumeQueueByMessageId.set(message.id, []);
-		}
+		// Don't stack resume requests. If a fence already exists for
+		// this message, an earlier request is in flight (or will be
+		// resolved by its fallback timer). Stacking would reset the
+		// timer on every reconnect and, under mixed-version deployments
+		// where an old backend doesn't echo request_id, leave the fence
+		// stuck with request_ids that never match.
+		if (resumeQueueByMessageId.has(message.id)) return;
+		resumeQueueByMessageId.set(message.id, []);
 		const existingTimer = resumeFenceTimerByMessageId.get(message.id);
 		if (existingTimer) clearTimeout(existingTimer);
 		resumeFenceTimerByMessageId.set(