-- Phase 4 deferred assessment columns. Do not DROP. Do not add passed/grade.

ALTER TABLE `ai_task_step`
    ADD COLUMN `expected_text` TEXT NULL COMMENT '范读原文（txt 契约，非 SD 路径）' AFTER `prompt_text`,
    ADD COLUMN `metrics` JSON NULL COMMENT '定量指标 [{method,value}]' AFTER `audio_id`,
    ADD COLUMN `assessed_at` BIGINT NULL COMMENT '后评估完成 epoch ms' AFTER `metrics`;