Two related bugs from the Slipknot album never finishing.
1) _poll_album_bundle_downloads hung when the peer stalled. The finish check
needs every transfer terminal (completed/failed); the #715 grace only covers
'slskd says Completed but file not on disk'. A transfer stuck InProgress /
Queued, or dropped by slskd, is none of those — so it blocked both the finish
AND the grace exit, and the poll spun to the full ~6h timeout.
Add a bundle-level stall guard: track a progress marker (#terminal transfers,
total bytes across pending). If NOTHING advances for _stall_grace (180s) —
no terminal transition AND no pending byte movement — the peer has stalled;
mark the stuck transfers failed so the existing finish/all-failed checks
resolve the bundle with whatever completed (missing tracks then fall back to
the per-track matcher). Conservative: only trips when EVERYTHING is frozen,
so a slow-but-progressing or still-queued transfer is unaffected.
2) Failed batches lingered in the UI forever ('No tracks loaded'). The
auto-cleanup gate removed only complete/error/cancelled phases — 'failed'
(e.g. an album-bundle hard failure) was missing, so it never aged out. Add
'failed' to the terminal set so it's removed after 5 minutes like the others.
Tests (tests/test_soulseek_album_poll_stall.py): stalled peer → gives up with the
completed subset (not the deadline); progressing bundle not falsely stalled;
all-stalled → empty; dropped transfers stall out; clean finish unaffected.
124 download/soulseek tests pass; ruff clean.
