Trashed artifacts past a ~3-day retention window are now purged automatically.
- storage.purge_expired_trash(): removes trash older than TRASH_RETENTION
(all users), tolerant of already-gone rows (concurrent-safe).
- spawn_trash_purge(): runs it on a daemon thread (manages/closes its own DB
connection), triggered by each delete so it's cron-less and off the request
thread. Inline fallback when AGENTFEED_ASYNC_PURGE is off (tests).
- Wired into both delete paths (API + session). Manual Empty Trash unchanged.
- Tests: purge removes expired-only; delete triggers the purge. 152 passing;
live delete verified with the thread enabled (204, server healthy).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>