Closing the dashboard tab or clicking outside the scan modal raised
ClientConnectionResetError out of scan_images and abandoned the scan
mid-batch, leaving a half-scanned database. Two overlapping scans could
also run at once.
- py/api/scan_job.py: ScanJob fans progress out to any number of SSE
subscribers (latest snapshot first, then live events)
- POST /prompt_manager/scan starts the scan as an asyncio task, or attaches
to the one already running; a write to a dead socket ends that stream
quietly while the scan continues
- GET /prompt_manager/scan/status reports the running flag and last event
- dashboard: dismissing the modal while a scan runs minimizes it to a
progress pill, the page re-attaches to a running scan after a reload,
a lost stream reconnects, and leaving the page mid-scan asks first