-- 全局视频转码租约。字段均可空，部署前后兼容；不改动任何已有素材 URL 或源文件。
ALTER TABLE "materials"
  ADD COLUMN IF NOT EXISTS "transcode_lease_token" TEXT,
  ADD COLUMN IF NOT EXISTS "transcode_lease_expires_at" TIMESTAMP(3);

CREATE INDEX IF NOT EXISTS "materials_transcode_lease_idx"
  ON "materials"("transcode_lease_expires_at", "transcode_lease_token");