ALTER TABLE `assets`
  ADD COLUMN `display_name` VARCHAR(255) NULL,
  ADD COLUMN `selection_status` VARCHAR(30) NOT NULL DEFAULT 'candidate',
  ADD COLUMN `selection_note` TEXT NULL,
  ADD COLUMN `metadata_json` JSON NULL;

CREATE INDEX `assets_project_id_selection_status_idx` ON `assets`(`project_id`, `selection_status`);