When a file is quarantined (AcoustID / integrity / bit-depth), the source
is moved away and _mark_task_quarantined sets _quarantine_entry_id on the
context. A second post_process_matched_download call with the same
file_path (caused by a monitor re-poll or concurrent dispatch before the
context is cleaned up) then hit the race guard — "source file gone, no
known destination" — and overwrote the in-flight retry with a failed status.
Fix: check _quarantine_entry_id before firing the race guard. If it is
set, the file is legitimately in quarantine and this is a stale duplicate;
return silently so the quarantine retry already in flight can proceed.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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