Both function bodies (_discovery_score_candidates and
_search_spotify_for_tidal_track) are byte-identical to the originals.
The shared matching_engine instance is injected via init() right after
_init_connection_test; the spotify proxy + _get_metadata_fallback_source
shim follow the same pattern used elsewhere.
web_server.py: 36019 → 35753 (-266 lines).
