since 9a0e3b40 persisted completed downloads in the Downloads view, the Clear Completed button
was hidden for those rows and clear-completed only pruned live session tasks. after a restart
the page filled with persisted completed downloads with no way to clear them.
now Clear Completed clears BOTH:
- live session completed/failed tasks (clear_completed_local, unchanged), AND
- the persisted download-history tail: new clear_completed_download_history() deletes every
library_history event_type='download' row, so the list actually empties and stays empty.
this includes unverified rows (the verification review queue) by design: on a library where
verification never confirmed the imports, ALL completed downloads are 'unverified', so preserving
them made the button a no-op. it only removes HISTORY rows — the actual files and their tracks
entries are untouched, so nothing in the library is lost, only the 'needs verification' flags.
the action confirms first (showConfirmDialog, destructive) and the button now shows whenever any
completed/failed row is present.
3 seam tests (clears all incl unverified; leaves non-download history; empty=0); reconcile +
orphan + JS integrity suites green.
d30273985f
