Register MusicBrainz as a first-class metadata source alongside Deezer, iTunes, Spotify, Discogs, and Hydrabase. Expose the shared client through metadata services, add the settings option, and expand the MusicBrainz search adapter with source-compatible artist, album, track, and detail methods.
Carry MusicBrainz IDs through similar-artist discovery, recommended artists, artist map serialization, and personalized playlist selection. Update DB migrations and lookup filters so similar_artist_musicbrainz_id is preserved on older schemas and used for source requirements and library exclusion.
Normalize MusicBrainz album adapter output for import context and add regression coverage for registry mapping, typed album conversion, and similar-artist filtering. Verified by user with 120 focused tests passing.
- Add similar artists fetching to web UI scan loop
- Add database migration for UNIQUE constraint on similar_artists table - Add source-agnostic /api/discover/album endpoint for iTunes support
- Fix NOT NULL constraint on discovery_recent_albums blocking iTunes albums
- Add fallback to watchlist artists when no similar artists exist
- Add /api/discover/refresh and /api/discover/diagnose endpoints
- Add retry logic with exponential backoff for iTunes API calls
- Ensure cache_discovery_recent_albums runs even when pool population skips
