-- Backfill `date_taken_source` for rows that pre-date the canonical-date
-- pipeline. Before the resolver landed, `image_exif.date_taken` could
-- only be populated via `exif::extract_exif_from_path` (kamadak-exif)
-- on the file-watcher, upload, or GPS-write paths. The resolver column
-- migration added `date_taken_source` defaulting to NULL, so every
-- historical row with a date is currently unlabelled — and the
-- per-tick drain skips them because its eligibility predicate is
-- `date_taken IS NULL OR date_taken_source = 'fs_time'`.
--
-- Label them `'exif'` once and let the drain take over from here. Safe
-- because every code path that wrote `date_taken` prior to the
-- resolver was a kamadak-exif read — there was no other source.
--
-- Idempotent: re-running this migration on a DB that has already been
-- backfilled is a no-op (the WHERE clause matches nothing the second
-- time around).
UPDATE image_exif
SET date_taken_source = 'exif'
WHERE date_taken IS NOT NULL
  AND date_taken_source IS NULL;