CREATE TABLE knowledge_domain (
    id               BIGINT AUTO_INCREMENT PRIMARY KEY,
    domain_id        VARCHAR(64)  NOT NULL UNIQUE COMMENT 'category 值，如 payment/infrastructure',
    description      VARCHAR(256) COMMENT '域描述，聚合自文档 summary',
    when_to_retrieve TEXT         COMMENT '域级检索时机，LLM 聚合生成',
    document_count   INT          NOT NULL DEFAULT 0 COMMENT '该域当前文档数',
    created_at       DATETIME     NOT NULL,
    updated_at       DATETIME     NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='知识域元数据，存储域级检索策略';