Add MusicBrainz watchlist artist ID storage, badges, linked-provider editing, and per-artist preferred source support.
Backfill watchlist MusicBrainz matches from already-enriched library artists so existing MusicBrainz worker matches appear in watchlist cards and settings.
Extend bulk watchlist add, liked artist matching, artist map source picking, and service status labels to recognize MusicBrainz, with regression tests for watchlist ID persistence and backfill.
The /api/library/watchlist-all-unwatched endpoint required the
user's currently active metadata source's ID column on each library
artist. A Spotify-primary user with library artists only matched
against iTunes or Deezer saw them silently skipped — surfacing on
Discord as "Library and Watchlist not syncing correctly". The per-
artist Enhanced View sync sometimes "fixed" them because it triggered
metadata enrichment that occasionally populated the missing Spotify
ID, but couldn't help artists Spotify simply doesn't carry.
Extracts the picker as a standalone helper so it can be tested
directly:
core/watchlist/source_picker.py:pick_artist_id_for_watchlist
Picks the active source first when available, then falls back through
spotify -> itunes -> deezer -> discogs in registration order. Empty
strings count as missing. Numeric IDs are coerced to str so SQLite's
TEXT columns store them in the same form library code reads back.
Returns (None, None) only when the artist has zero source IDs — the
only legitimate skip reason now.
Adds 10 regression tests covering active-source priority for each
supported primary, fallback ordering through every secondary, the
zero-IDs base case, unrecognized active source (e.g. hydrabase still
falls through), empty-string handling, and numeric coercion.
Broque Thomas