修复老库群公告字段缺失导致群详情报错

变更项：
1. 新增字段探测与补列逻辑：启动时通过 information_schema 检查 t_chatrooms.chat_room_announcement，不依赖 ADD COLUMN IF NOT EXISTS。
2. save_chatroom_info 改为字段存在才写入群公告，避免 Unknown column。
3. get_chatroom_profile 增加降级查询：字段不存在时返回空公告，不再直接引用缺失列。
4. 增加字段可用性缓存与中文注释，降低重复探测开销。

db/contacts_db.py

@@ -19,6 +19,52 @@ class ContactsDBOperator(BaseDBOperator):
     def __init__(self, db_manager: DBConnectionManager):
         super().__init__(db_manager)
         self.LOG = logger
+        # 缓存群公告字段是否存在，避免反复查询 information_schema。
+        self._chatroom_announcement_column_ready: Optional[bool] = None
+
+    def _column_exists(self, table_name: str, column_name: str) -> bool:
+        """检查当前数据库中指定表字段是否存在。"""
+        try:
+            sql = """
+            SELECT COUNT(1) AS cnt
+            FROM information_schema.COLUMNS
+            WHERE TABLE_SCHEMA = DATABASE()
+              AND TABLE_NAME = %s
+              AND COLUMN_NAME = %s
+            """
+            result = self.execute_query(sql, (table_name, column_name), fetch_one=True) or {}
+            return int(result.get("cnt") or 0) > 0
+        except Exception as e:
+            self.LOG.error(f"检查字段存在性失败: {table_name}.{column_name}, error={e}")
+            return False
+
+    def _ensure_chatroom_announcement_column(self) -> bool:
+        """确保群公告字段存在；老库不支持 IF NOT EXISTS 时也可兼容。"""
+        if self._chatroom_announcement_column_ready is True:
+            return True
+        if self._chatroom_announcement_column_ready is False:
+            return False
+
+        # 先探测：存在则直接标记成功。
+        if self._column_exists("t_chatrooms", "chat_room_announcement"):
+            self._chatroom_announcement_column_ready = True
+            return True
+
+        # 再补列：不使用 IF NOT EXISTS，兼容较低版本 MySQL。
+        alter_sql = """
+        ALTER TABLE t_chatrooms
+        ADD COLUMN chat_room_announcement TEXT COMMENT '群公告内容'
+        """
+        ok = self.execute_update(alter_sql)
+        if ok or self._column_exists("t_chatrooms", "chat_room_announcement"):
+            self._chatroom_announcement_column_ready = True
+            self.LOG.info("已确认 t_chatrooms.chat_room_announcement 字段可用")
+            return True
+
+        # 失败时降级，后续查询将不再引用该字段，避免 Unknown column。
+        self._chatroom_announcement_column_ready = False
+        self.LOG.warning("t_chatrooms.chat_room_announcement 字段不可用，将按无公告字段模式运行")
+        return False
 
     def _ensure_table_exists(self):
         """确保联系人表存在"""
@@ -109,11 +155,8 @@ class ContactsDBOperator(BaseDBOperator):
                 UNIQUE KEY `idx_chatroom_id` (`chatroom_id`)
             ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='微信群信息表';
             """)
-            # 兼容历史库：老版本表可能没有群公告字段，这里启动时自动补齐。
-            self.execute_update("""
-            ALTER TABLE t_chatrooms
-            ADD COLUMN IF NOT EXISTS chat_room_announcement TEXT COMMENT '群公告内容'
-            """)
+            # 兼容历史库：启动时补齐群公告字段；失败时后续逻辑自动降级兼容。
+            self._ensure_chatroom_announcement_column()
             self.LOG.info("成功创建或确认微信群信息表存在")
         except Exception as e:
             self.LOG.error(f"创建微信联系人表或群成员表失败: {e}")
@@ -542,12 +585,14 @@ class ContactsDBOperator(BaseDBOperator):
                 'remark_quan_pin': get_str('RemarkQuanPin'),
                 'chat_room_notify': chatroom_data.get('ChatRoomNotify', 0),
                 'chat_room_owner': chatroom_data.get('ChatRoomOwner', ''),
-                'chat_room_announcement': announcement,
                 'small_head_img_url': chatroom_data.get('SmallHeadImgUrl', ''),
                 # 成员列表可选存储为JSON字符串
                 'member_list': json.dumps(chatroom_data.get('NewChatroomData', {}).get('ChatRoomMember', []),
                                           ensure_ascii=False)
             }
+            # 字段存在才写群公告，避免老库 Unknown column。
+            if self._ensure_chatroom_announcement_column():
+                data['chat_room_announcement'] = announcement
 
             fields = ', '.join(data.keys())
             placeholders = ', '.join(['%s'] * len(data))
@@ -708,13 +753,19 @@ class ContactsDBOperator(BaseDBOperator):
     def get_chatroom_profile(self, chatroom_id: str) -> Dict[str, Any]:
         """获取群资料（群公告、群主、管理员、成员数）用于通讯录详情展示。"""
         try:
+            # 公告字段在老库可能不存在：不存在则降级为空串，避免 SQL 报错。
+            announcement_expr = (
+                "c.chat_room_announcement"
+                if self._ensure_chatroom_announcement_column()
+                else "''"
+            )
             # 先取群基础信息 + 群主展示名 + 成员数。
-            info_sql = """
+            info_sql = f"""
             SELECT
                 c.chatroom_id,
                 c.nick_name,
                 c.chat_room_owner,
-                c.chat_room_announcement,
+                {announcement_expr} AS chat_room_announcement,
                 COALESCE(NULLIF(owner_member.display_name, ''), owner_member.nick_name, c.chat_room_owner, '') AS owner_name,
                 (
                     SELECT COUNT(*)