Final lift in the PR5 discovery-workers series. Pulls the 328-line
library quality scanner 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 quality scanner does:
1. Reset scanner state (counters, results), load quality profile +
minimum acceptable tier from QUALITY_TIERS.
2. Load tracks from DB based on scope:
- 'watchlist' → tracks for watchlisted artists only.
- other → all library tracks.
3. For each track:
- Stop-request gate (state['status'] != 'running').
- Quality-tier check via _get_quality_tier_from_extension(file_path).
- Skip tracks meeting standards (tier_num <= min_acceptable_tier).
- For low-quality tracks: matching_engine search query gen, score
candidates against Spotify (artist + title similarity, album-type
bonus), pick best match >= 0.7 confidence.
- On match: add full Spotify track to wishlist via
`wishlist_service.add_spotify_track_to_wishlist` with
source_type='quality_scanner' and a source_context that captures
original file_path, format tier, bitrate, and match confidence.
4. After all tracks: status='finished', progress=100, activity feed
entry, emit `quality_scan_completed` event for automation engine.
5. On critical exception: status='error', error message captured.
Wishlist service interaction is via the public
`add_spotify_track_to_wishlist` API only — no overlap with kettui's
planned `core/wishlist/` package extraction (the import lives inside
the function, exactly as in the original, and will follow whatever
path that package takes).
Dependencies injected via `QualityScannerDeps` (8 fields) —
quality_scanner_state dict, quality_scanner_lock, QUALITY_TIERS
constant, spotify_client, matching_engine, automation_engine, plus 2
callable helpers (get_quality_tier_from_extension, add_activity_item).
Diff vs original after `deps.X` → global X normalization is **zero
differences** — 328 lines orig = 328 lines lifted, byte-identical body
(including all whitespace, comments, log strings, and the inline
`from core.wishlist_service import get_wishlist_service` /
`from database.music_database import MusicDatabase` imports at the
top of the function).
Tests: 11 new under tests/discovery/test_discovery_quality_scanner.py
covering state init/reset, no-watchlist-artists short-circuit,
unauthenticated Spotify error, high-quality skip, low-quality search
trigger, match → wishlist add (with full source_context payload),
no-match no-add, mid-loop stop request, completion phase + progress,
automation engine event emission, all-library scope load.
Full suite: 1152 passing (was 1141). Ruff clean.
End of the PR5 series — `web_server.py` lost ~328 lines on this commit
alone; total trim across PR5a–PR5h is ~2,400 lines of discovery worker
code moved into focused `core/discovery/*.py` modules. The remaining
discovery-adjacent worker `_process_watchlist_scan_automatically` was
deliberately deferred to avoid overlap with kettui's planned wishlist
extraction.
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