-- Manual date_taken override: when an operator overrides a row's date via
-- POST /image/exif/date, the prior `(date_taken, date_taken_source)` is
-- snapshotted into these columns and the live columns hold the new value
-- with `date_taken_source = 'manual'`. POST /image/exif/date/clear restores
-- the pair and nulls the originals.
--
-- The waterfall source-name set is now:
--   'exif' | 'exiftool' | 'filename' | 'fs_time' | 'manual'
--
-- The `idx_image_exif_date_backfill` partial index already filters to
-- `date_taken IS NULL OR date_taken_source = 'fs_time'`, so 'manual' rows
-- are naturally excluded from the per-tick backfill drain — no index
-- change needed.
ALTER TABLE image_exif ADD COLUMN original_date_taken BIGINT;
ALTER TABLE image_exif ADD COLUMN original_date_taken_source TEXT;