RuntimeError: Task attached to a different loop

Root cause

Background dispatcher queue and worker task were initialized by a session-scoped async fixture during FastAPI startup, then pytest-asyncio reset/recreated the event loop for the test function. The request handler awaited a queue Future bound to the stale loop.

Minimal fix

Change the FastAPI app/client fixture to function scope, create the dispatcher only after pytest has established the active test event loop, and explicitly await the app lifespan startup before issuing requests. Avoid creating asyncio.Queue or background tasks at import time or in session-scoped async fixtures.