Summary

• FixesAttributeError:'coroutine' object has no attribute 'result' when usinglangchain.agents.create_agent with async execution (ainvoke) and custom async middleware #34234
• Adds_normalize_to_model_response_async() to detect when async middleware returns a coroutine instead of ModelResponse/AIMessage
• Auto-awaits the coroutine with a helpful warning message guiding users to fix their code

Problem

When users implementawrap_model_call and forget to await the handler:

asyncdefawrap_model_call(self,request,handler):returnhandler(request)# Missing await!

This causesAttributeError: 'coroutine' object has no attribute 'result' which is confusing.

Solution

The fix detects this scenario and:

1. Auto-awaits the coroutine to prevent the crash
2. Emits a warning explaining the issue and how to fix it

Test plan

• Added tests for missing await scenarios (single/multiple middleware)
• Added test verifying proper await does not emit warning
• All existing middleware tests pass (167 tests)
• Linting passes
• Type checking passes

AI agents were involved in developing this contribution.