Eighth cluster, the heavyweights (~110 lines each). The fix-modal
update_<source>_discovery_match for the four sources with the identical
structure (Tidal, Deezer, Qobuz, Spotify-Public) ->
core.discovery.endpoints.update_discovery_match(...), wired via
_update_source_discovery_match. Applies the user-selected Spotify track to the
discovery result (status/artist/album/duration/spotify_data/match-count) and
writes the manual fix to the discovery cache.
Per-source pieces are params:
- source_log_label / error_label.
- original_track_key ('tidal_track' / 'deezer_track' / ...).
- original_artist_getter: Tidal handles string-or-object artists
(first_artist_str_or_obj); the rest assume strings (first_artist_plain).
- web_server helpers (join/extract artist, build_fix_modal_spotify_data,
cache-key, get_database, active-discovery-source) injected.
- get_json passed as a callable and invoked INSIDE the try, preserving the
original's "request.get_json() inside try" behavior (malformed body -> 500).
NOT folded in (genuinely divergent): iTunes-Link (saves spotify_data directly
via a different cache signature), YouTube (multi-key original_track fallback),
ListenBrainz (entirely different unmatch-capable structure, no cache write),
Beatport.
Tests: +9 (extractors; 400/404/400 guards; full happy path with result
mutation + duration formatting + match-count + cache-save args; no-increment
when already found; cache error swallowed; get_json raise -> 500). Full
discovery suite: 198 passed.
web_server.py: -400 lines.
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