Force rescan was metadata-only: updateMediaItem never touched the
hash identifiers, so a force scan could not backfill file_sha256 for
items imported before hashing existed (or where extraction originally
failed). Those items were invisible to content dedup and SHA-256
device matching with no way to fix short of delete + re-import.
processMediaFile now refreshes hash identifiers in three cases:
- force rescan (the admin Scan button becomes the backfill tool)
- file size change (stored hash is stale - the bytes changed)
- unchanged file with no stored hash (ordinary scans self-heal the
legacy backlog incrementally, no admin action required)
Each recompute runs recordHashConflictIfAny: when the freshly stored
hash is now shared by more than one item in the library, the group is
upserted into hash_conflicts for the admin Hash Conflicts page. The
upsert is a no-op for already-tracked groups, so resolved 'keep both'
decisions stick.
Also extract a package-level computeFileSHA256 (the scanner method
now delegates to it) so the startup backfill service can hash files
without a scanner instance.
john-okeefe
77990d0dc0