The manual wishlist download endpoint blocked the request thread on a
slow library-cleanup pass before submitting the batch — for a 24-track
wishlist that's ~50 per-track DB lookups serialised in the request
handler, taking 30+ seconds before the frontend got a response. The
modal sat at "Pending..." with no progress visible the whole time.
Split start_manual_wishlist_download_batch into:
1. SYNC path (request handler):
- Generate batch_id, create download_batches entry with phase=analysis
and analysis_total=0 placeholder.
- Submit a single bg job (`_prepare_and_run_manual_wishlist_batch`) to
the missing-download executor.
- Return 200 with batch_id immediately. Frontend can start polling
/api/active-processes status right away.
2. BG path (executor thread):
- db.remove_wishlist_duplicates (slow-ish, single SQL)
- remove_tracks_already_in_library (the slow one — per-track DB checks)
- wishlist_service.get_wishlist_tracks_for_download
- sanitize + dedupe + filter (track_ids / category)
- Update batch.analysis_total with the real filtered count
- add_activity_item("Wishlist Download Started", ...)
- run_full_missing_tracks_process (master worker)
Edge case: if cleanup empties the wishlist, the bg job marks the batch
phase='complete' with error='No tracks in wishlist' (instead of the old
synchronous 400 response). Frontend status poll picks this up and the
modal can close cleanly.
Tests: existing 2 manual-download tests updated to drive the bg job
explicitly via a new `_run_submitted_bg_job` helper. Added 2 new tests:
- `..._returns_immediately_with_placeholder` — proves the sync path
doesn't trigger any cleanup or master-worker calls; analysis_total=0.
- `..._marks_batch_complete_when_wishlist_empty_after_cleanup` —
cleanup empties the list, master worker never invoked, batch ends
with phase='complete'.
Full suite: 1232 passing (was 1230). Ruff clean.
6a25dcd49e