// Existing immutable snapshots retain unknown context metadata; never fabricate old counts.
exports.up = pgm => pgm.sql(`
  ALTER TABLE generated_image_jobs ADD context_included INTEGER, ADD context_total INTEGER,
    ADD CONSTRAINT generated_image_context_counts CHECK (
      (context_included IS NULL AND context_total IS NULL) OR
      (context_included IS NOT NULL AND context_total IS NOT NULL AND context_included >= 0 AND context_total >= context_included));
  CREATE FUNCTION guard_generated_image_context() RETURNS trigger LANGUAGE plpgsql AS $$
  BEGIN
    IF (NEW.context_included, NEW.context_total) IS DISTINCT FROM (OLD.context_included, OLD.context_total) THEN
      RAISE EXCEPTION 'Image context metadata is immutable';
    END IF;
    RETURN NEW;
  END; $$;
  CREATE TRIGGER generated_image_context_immutable BEFORE UPDATE ON generated_image_jobs FOR EACH ROW EXECUTE FUNCTION guard_generated_image_context();
`);
exports.down = pgm => pgm.sql(`
  DROP TRIGGER generated_image_context_immutable ON generated_image_jobs;
  DROP FUNCTION guard_generated_image_context();
  ALTER TABLE generated_image_jobs DROP context_included, DROP context_total;
`);