fix exception & paramer chatbot

app.py

@@ -575,13 +575,8 @@ async def stream_agent_response(question: str, chat_history: List) -> List[Dict]
         
     except Exception as e:
         error_msg = f"## ❌ Error\n\nOcurrió un error al procesar tu solicitud:\n\n```\n{str(e)}\n```"
-        if "assistant_message" in locals():
-            assistant_message["content"] = error_msg
-        else:
-            assistant_message = {"role": "assistant", "content": error_msg}
-        
         logger.error(f"Error in stream_agent_response: {str(e)}", exc_info=True)
-        return [assistant_message]
+        return [(None, error_msg)]
 
 # Custom CSS for the app
 custom_css = """
@@ -692,7 +687,9 @@ def create_ui():
                 height=600,
                 render_markdown=True,  # Enable markdown rendering
                 show_label=False,
-                show_share_button=False
+                show_share_button=False,
+                container=True,
+                layout="panel"  # Better layout for messages
             )
         
         # Input area