First lift in the new PR5 discovery-workers series. Pulls the 448-line
playlist sync background worker out of `web_server.py` into its own
focused module under `core/discovery/`. Pure 1:1 lift — wrappers keep
the original entry-point name so the four callers
(`sync_executor.submit(_run_sync_task, ...)`) continue to work without
changes.
What the sync worker does:
1. Convert frontend JSON tracks → SpotifyTrack/SpotifyPlaylist objects.
2. Normalize artist/album shapes for downstream wishlist parity.
3. Wire a progress_callback that updates `sync_states` + automation card.
4. Patch sync_service for database-only fallback when no media server is
connected.
5. `run_async(sync_service.sync_playlist(...))` and capture the result.
6. Update sync_states to 'finished', push playlist poster image to
Plex / Jellyfin / Emby, record sync history (with re-sync vs new-sync
branching), emit `playlist_synced` event for automation engine, and
persist sync status with a tracks_hash for smart-skip on the next
scheduled sync.
7. On exception → mark error in sync_states + automation; finally clear
progress callback + drop `_original_tracks_map` from sync_service.
Dependencies injected via `SyncDeps` (11 fields) — config_manager,
sync_service, plex_client, jellyfin_client, automation_engine, run_async,
record_sync_history_start, update_automation_progress,
update_and_save_sync_status, sync_states dict, sync_lock. The only
structural drift from a pure paste is the top-of-function variable
binding: original used `global sync_states, sync_service`, lifted version
rebinds them as locals from deps (`sync_states = deps.sync_states` etc.)
since the names aren't module-level in the new file. Same behaviour
otherwise — diff against the original after `deps.X` → global X
normalization is **zero differences**.
Tests: 18 new under tests/discovery/test_discovery_sync.py covering
sync history recording (new + resync), setup error path (with and
without automation_id), missing sync_service handling, sync_playlist
exception handling, successful sync state transition, unmatched-tracks
summary, playlist image upload (plex + jellyfin + zero-synced gate),
automation engine emit, automation progress finished call, sync history
DB persistence (completion + match_details), tracks_hash persistence,
and finally-block cleanup (callback clear + map drop).
Full suite: 1068 passing (was 1050). Ruff clean.
Kicks off the PR5 series — 9 discovery workers totaling ~2,400 lines
across `_run_sync_task`, `_run_*_discovery_worker` family,
`_run_quality_scanner`, and `_process_watchlist_scan_automatically`.
Wishlist-related extractions deliberately skipped to avoid overlap with
kettui's planned `core/wishlist/` package.
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