-- PBKDF2 哈希长度超过 64 时拒绝回退，避免截断管理员密码。
DELIMITER //
CREATE PROCEDURE rollback_v2_p4_admin()
BEGIN
    IF EXISTS (SELECT 1 FROM admin_user WHERE CHAR_LENGTH(password_hash) > 64) THEN
        SIGNAL SQLSTATE '45000'
            SET MESSAGE_TEXT = 'V2 rollback blocked: PBKDF2 password hashes already exist';
    END IF;
    ALTER TABLE admin_user
        MODIFY COLUMN password_hash CHAR(64) NOT NULL COMMENT '密码 SHA-256 hex';
END //
DELIMITER ;

CALL rollback_v2_p4_admin();
DROP PROCEDURE rollback_v2_p4_admin;