Root cause: When album downloads completed, the frontend immediately closed
the modal and called /api/playlists/cleanup_batch, which deleted the batch
from memory. The wishlist processing thread (submitted to executor) would
then try to access the batch and fail silently because it was already deleted.
This explains why:
- Wishlist auto-processing worked (different timing/3-second delay)
- Manual "Add to Wishlist" button worked (different code path, before downloads)
- Album modal failed tracks didn't get added (race condition)
The fix prevents batch cleanup until wishlist processing completes:
Backend (web_server.py):
1. Mark wishlist_processing_started=True when submitting processing job
2. Mark wishlist_processing_complete=True when processing finishes
3. Block cleanup endpoint if processing in progress (return 202)
Frontend (script.js):
4. Handle 202 response and retry cleanup after 2-second delay
This eliminates the race condition while maintaining async processing and
ensuring all failed/cancelled tracks are properly added to the wishlist.
Broque Thomas
c0c05c7b89