-- 016: 为 conversations 增加 ext_agent_conversation_id 列
-- 用途：外部 Agent(Dify/Coze) 远程调用时保存其平台侧 conversation_id，
--       以维持多轮上下文。n8n(无平台会话态) 不使用该列。
-- 幂等：列已存在则跳过。
SET @col = (SELECT COUNT(*) FROM information_schema.columns
            WHERE table_schema = DATABASE()
              AND table_name = 'conversations'
              AND column_name = 'ext_agent_conversation_id');
SET @sql = IF(@col = 0,
    'ALTER TABLE conversations ADD COLUMN ext_agent_conversation_id VARCHAR(128) NULL COMMENT \'外部Agent(Dify/Coze)会话ID，用于维持多轮上下文\'',
    'SELECT 1');
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;