RuntimeError: Task attached to a different loop

Root cause

Background dispatcher startup task is created by a session-scoped FastAPI app/client fixture before pytest-asyncio resets the event loop for the test function. The route later awaits that task from the function's active loop, causing the cross-loop RuntimeError.

Minimal fix

Make the async app/client fixture function-scoped and perform FastAPI lifespan startup inside the same loop used by each test. Avoid creating dispatcher background tasks at import time or in session-scoped fixtures; initialize them during awaited startup and shut them down in fixture teardown.