The library holds the same RAW in several folders: a dated folder, a
bck/ beside it, a renamed Darktable export tree. dr_catalog::duplicates
is the catalog half of consolidating them (#67).
candidates() is one grouped query over root, camera, capture instant and
size, joined back for the rows; count() is the same grouping under
COUNT. On a copy of the reference catalog (23,582 images) both take
10-35 ms and find 1,836 groups holding 3,379 spare copies.
survivor() prefers a copy outside a backup-looking folder, then one
still named the way the camera named it, then the oldest, then the
lowest id.
consolidate() re-checks the plan against the catalog, merges the copies'
judgements onto the survivor (highest rating, keywords unioned,
collections unioned with the survivor keeping its place, a flag or label
the copies agree on, faces via faces::carry_onto_copy) and records the
copies as trashed, all in one transaction, so a failure part way leaves
the group untouched. preview() runs the same code and rolls it back.
Sameness probes are kept in dedup_probes, created on first use rather
than by a migration: a schema bump would make older builds refuse this
catalog's snapshot at sync. trash::record_trashed_within lets the trash
write share the merge's transaction.
