Line-by-line review of the search lift caught one drift: cache.get_cache_key
was coercing falsy provider returns ('', None, 0) to 'unknown' / False.
Original web_server.py only fell back to those sentinels on exception, not
on falsy success values.
Real-world impact: low — get_active_media_server() and get_primary_source()
return non-empty strings in practice. But cache keys are tuples with no
schema enforcement, so any drift here can silently fragment the cache.
Restored 1:1 parity with original semantics.
Added test covering the falsy-success path so this can't drift again.
789 tests pass, ruff clean.
47b4663091