`_read_on_pods` returned None in silence when no pod could serve, and the caller
then read the document locally. So an install configured for the pod-side
pipeline could fall back on EVERY request and look exactly like a success: the
OCR works, the text is right, and the operator concludes the new path is working
when it has never run once. A test that cannot distinguish the two paths proves
nothing about either.

Both paths now announce themselves in one line -- the fallback naming the CAUSE
("placement answered 'local' — nothing rented, or the pool could not serve")
rather than only the effect, and the success saying the pages were rasterised
and read on the pods rather than here.

Found while answering "can I launch the new OCR to test?", which is exactly when
it mattered: the answer was yes, and the test would have been uninterpretable.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HXRMe9ZPUQCCCtBai9uqt3