Fix: capture main_agent before SSE generator to avoid lost app context

Quart exits the request/app context before iterating the SSE response
body, so current_app inside event_generator() raised "Not within an app
context". Capture the reference before the generator is defined. Also
add return after the exception error yield to prevent falling through to
a second "No response generated" event on the same stream.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

blueprints/conversation/__init__.py

@@ -247,6 +247,10 @@ async def stream_query():
             "system_prompt": system_prompt,
         }
     }
+    # Capture the agent reference while the request/app context is still active.
+    # Quart exits the app context before iterating the SSE response body, so
+    # current_app cannot be accessed inside event_generator().
+    main_agent = current_app.main_agent
 
     async def event_generator():
         final_message = None
@@ -305,7 +309,7 @@ async def stream_query():
             )
 
         try:
-            aiter = current_app.main_agent.astream_events(
+            aiter = main_agent.astream_events(
                 payload, version="v2", config=agent_config
             ).__aiter__()
             while True:
@@ -414,6 +418,7 @@ async def stream_query():
             count_result(stream=True, result="error")
             _log_summary(error=str(e))
             yield f"data: {json.dumps({'type': 'error', 'message': str(e)})}\n\n"
+            return
 
         final_message = final_message or streamed
         if final_message: