Exception Not Propagating in CrewAI Flow with @listen, But Works with @start

Crews
,
1

I have encapsulated a basic CrewAI Flow inside a FastAPI endpoint, but I’m encountering unexpected behavior: exceptions raised in the generate_fun_fact method (decorated with @listen) are not properly propagated. As a result, my /process_email endpoint incorrectly returns a 200 status even in cases where it should fail.

Here’s a minimal reproducible example:

from crewai.flow.flow import Flow, listen, start
from litellm import completion

class ExampleFlow(Flow):
    model = "gpt-4o-mini"

    @start()
    async def start(self):
        pass

    @listen(start)
    async def generate_fun_fact(self):
        try: 
            assert False  # This should raise an AssertionError
        except Exception as e:
            print(f"Error in generate_fun_fact: {e}")
            raise

@router.post("/process_email/{uuid}") 
async def process_email(uuid: str, request: Request):
    try:
        _result = await ExampleFlow().kickoff_async()
        return 'Workflow Completed Successfully'
    except Exception as e:
        log.error(f"Unexpected error in test: {str(e)}")
        raise EmailProcessingException(message=str(e))

The Issue:

  • When an exception is raised inside a method decorated with @listen, it does not propagate correctly, causing the FastAPI endpoint to return 200 OK instead of failing as expected.
  • However, when the method raising the exception is decorated with @start, the exception is properly handled.

Question:

  • Is this a bug in CrewAI?
  • Does anyone know of a workaround to ensure exceptions inside @listen handlers propagate correctly?