Seventh lift in the PR5 discovery-workers series. Pulls the 286-line
ListenBrainz discovery worker out of `web_server.py` into its own
focused module under `core/discovery/`. Pure 1:1 lift — wrapper keeps
the original entry-point name.
What the ListenBrainz discovery worker does:
1. Pause enrichment workers (release shared resources).
2. For each ListenBrainz track:
- Cancellation gate (state['phase'] != 'discovering').
- Discovery cache lookup; cache hit short-circuits the search.
- Strategy 1: matching_engine search queries with confidence scoring
against Spotify (preferred) or iTunes (fallback).
- Strategy 2: swapped artist/title query.
- Strategy 3: album-based query (uses album_name when available —
unique to LB, since YouTube tracks don't have album metadata).
- Strategy 4: extended search with limit=50.
- On match → save to discovery cache with image extracted from album
images or matched_track.image_url fallback.
- On miss → Wing It stub stored as 'wing-it' status.
3. After all tracks: phase='discovered', status='complete', activity feed
entry mentioning 'ListenBrainz Discovery Complete'.
4. On error: state['status']='error', phase='fresh'.
5. Finally: resume enrichment workers.
Dependencies injected via `ListenbrainzDiscoveryDeps` (16 fields) —
listenbrainz_playlist_states, spotify_client, matching_engine, plus 13
callable helpers (pause/resume enrichment, get_active_discovery_source,
get_metadata_fallback_client, get_discovery_cache_key, get_database,
validate_discovery_cache_artist, extract_artist_name,
spotify_rate_limited, discovery_score_candidates, get_metadata_cache,
build_discovery_wing_it_stub, add_activity_item).
Diff vs original after `deps.X` → global X normalization is **zero
differences** — 286 lines orig = 286 lines lifted, byte-identical body
(including all whitespace, comments, log strings).
Pre-existing bug preserved (not fixed): if `listenbrainz_playlist_states[
state_key]` raises KeyError on entry, the outer except handler tries to
mutate `state` which is unbound → secondary UnboundLocalError. Same bug
in the original (and the YouTube discovery worker). Documented here for
future cleanup but out of scope for the lift.
Tests: 11 new under tests/discovery/test_discovery_listenbrainz.py
covering cache hit short-circuit, Strategy 1 confidence match, Wing It
fallback, iTunes fallback (Spotify unauthenticated and rate-limited),
cancellation (phase change), completion phase update, activity feed
entry, per-track error handling, float duration_ms tolerance (regression
for the :02d format crash fixed earlier), enrichment workers resume on
finally.
Full suite: 1141 passing (was 1130). Ruff clean.
c9108ef2fe