diff --git a/src/blackboard/db.py b/src/blackboard/db.py
index 5cadaed..2d9edd6 100644
--- a/src/blackboard/db.py
+++ b/src/blackboard/db.py
@@ -103,6 +103,9 @@ def _migrate_v28(conn: sqlite3.Connection) -> None:
             CREATE INDEX IF NOT EXISTS idx_tasks_parent ON tasks(parent_task);
             CREATE INDEX IF NOT EXISTS idx_tasks_current_agent ON tasks(current_agent);
         """)
+
+
+def _safe_add_column(conn: sqlite3.Connection, table: str,
                      column: str, col_type: str) -> None:
     """安全添加列（已存在则跳过）"""
     try: