-- True-instant date contract (ADR-0001 / spec #113, tickets #114 + #115).
--
-- image_exif gains the new-contract columns alongside the untouched legacy
-- `date_taken`:
--   date_utc              — true UTC instant (unix seconds) under the new
--                           contract; NULL while the row is still on the
--                           legacy convention (drain pending).
--   camera_offset_minutes — camera local − UTC in minutes that produced
--                           date_utc (NULL for direct-UTC branches).
--   date_taken_tz_source  — why the offset is what it is:
--                           offset_tag | gps | assumed_server | utc_direct
--                           | manual.
--
-- Manual date edits (ticket #115) write the new-contract triple alongside
-- the legacy pair and must be revertible, so image_exif also snapshots the
-- pre-override new-contract columns next to the existing legacy snapshot
-- pair (original_date_taken / original_date_taken_source):
--   original_date_utc / original_camera_offset_minutes /
--   original_date_taken_tz_source.
--
-- All columns are additive and nullable; population happens at runtime
-- (ingest + the per-tick backfill drains), so no backfill SQL is needed
-- here. user_ai_prefs gains the DST-proof display zone (IANA name); the
-- legacy tz_offset_minutes column stays frozen for rollback.

ALTER TABLE image_exif ADD COLUMN date_utc BIGINT;
ALTER TABLE image_exif ADD COLUMN camera_offset_minutes INTEGER;
ALTER TABLE image_exif ADD COLUMN date_taken_tz_source TEXT;
ALTER TABLE image_exif ADD COLUMN original_date_utc BIGINT;
ALTER TABLE image_exif ADD COLUMN original_camera_offset_minutes INTEGER;
ALTER TABLE image_exif ADD COLUMN original_date_taken_tz_source TEXT;
ALTER TABLE user_ai_prefs ADD COLUMN display_tz TEXT;