fix async error

app.py

@@ -213,17 +213,18 @@ async def main(message: cl.Message):
     try:
         lcel_rag_chain = cl.user_session.get("lcel_rag_chain")
 
+        # Create a message to stream to
+        msg = cl.Message(content="")
+        await msg.send()
+
         # Get the response as a single string
         response = await cl.make_async(lcel_rag_chain.invoke)(
             {"query": message.content},
             config=RunnableConfig(callbacks=[cl.LangchainCallbackHandler()]),
         )
         
-        # Create and send the message with the response
-        await cl.Message(
-            content=response,
-            author="Paul Graham Essay Bot"
-        ).send()
+        # Update the message with the complete response
+        await msg.update(response)
 
     except Exception as e:
         error_message = str(e)