`FromDI` fails with an `AttributeError` on `None` when the DI middleware never ran for a message

[lesnik512]

What

Dependency.__call__ reads the request container out of FastStream's ContextRepo:

request_container: Container = context.get(_REQUEST_CONTAINER_KEY)
return self.marker.resolve(request_container)

ContextRepo.get returns None for a key nobody set, so when the DI middleware did not run for a message the user sees modern-di's internals fail on the next line:

AttributeError: 'NoneType' object has no attribute 'resolve_dependency'

Nothing in that message points at this package, at setup_di, or at app startup.

When it happens

• FromDI is used on an app where setup_di was never called.
• The app was never started, so the on_startup hook that installs the middleware (fix: install the DI middleware on every broker, on startup #52) did not run. The common form is a test that enters TestNatsBroker(broker) without TestApp(app); the modern-di docs already warn about that pairing, but the error itself does not.

Before #52 this was also what a subscriber on any broker but the first produced (#42).

Proposal

Check for None in Dependency.__call__ and raise a RuntimeError that says the request container is missing for this message and names the two fixes: call setup_di(app, container) on the app that owns the broker, and start the app (pair the test broker with TestApp in tests).

One failing test first, in tests/test_faststream_di.py, for each of the two triggers above.