diff --git a/src/blackboard/db.py b/src/blackboard/db.py
index a61d663..090087f 100644
--- a/src/blackboard/db.py
+++ b/src/blackboard/db.py
@@ -64,53 +64,54 @@ def _migrate_v28(conn: sqlite3.Connection) -> None:
         conn.execute("DROP TABLE IF EXISTS tasks_v28")
         # 迁移期间禁用 FK 检查（DROP TABLE tasks 会触发 events FK 约束）
         fk_was_on = conn.execute("PRAGMA foreign_keys").fetchone()[0]
-        conn.execute("PRAGMA foreign_keys = OFF")
-        conn.executescript("""
-            CREATE TABLE tasks_v28 (
-                id TEXT PRIMARY KEY,
-                title TEXT NOT NULL,
-                description TEXT,
-                status TEXT NOT NULL DEFAULT 'pending' CHECK (status IN ('pending','claimed','working','review','paused','escalated','waiting_human','done','failed','blocked','cancelled')),
-                assignee TEXT,
-                assigned_by TEXT,
-                depends_on TEXT,
-                parent_task TEXT,
-                priority INTEGER NOT NULL DEFAULT 5,
-                task_type TEXT,
-                created_at TEXT NOT NULL DEFAULT (datetime('now')),
-                updated_at TEXT NOT NULL DEFAULT (datetime('now')),
-                claimed_at TEXT,
-                started_at TEXT,
-                completed_at TEXT,
-                deadline TEXT,
-                retry_count INTEGER NOT NULL DEFAULT 0,
-                max_retries INTEGER NOT NULL DEFAULT 2,
-                must_haves TEXT,
-                risk_level TEXT DEFAULT 'standard',
-                estimated_duration_minutes INTEGER,
-                escalated INTEGER DEFAULT 0,
-                current_agent TEXT,
-                previous_agent TEXT,
-                next_capability TEXT,
-                stage TEXT,
-                stages_json TEXT DEFAULT '[]',
-                archived INTEGER DEFAULT 0,
-                archived_at TEXT
-            );
-            INSERT INTO tasks_v28 SELECT * FROM tasks;
-            DROP TABLE tasks;
-            ALTER TABLE tasks_v28 RENAME TO tasks;
-        """)
-        # 重建索引
-        conn.executescript("""
-            CREATE INDEX IF NOT EXISTS idx_tasks_status ON tasks(status);
-            CREATE INDEX IF NOT EXISTS idx_tasks_assignee ON tasks(assignee);
-            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);
-        """)
-        # 恢复 FK 检查
-        if fk_was_on:
-            conn.execute("PRAGMA foreign_keys = ON")
+        try:
+            conn.execute("PRAGMA foreign_keys = OFF")
+            conn.executescript("""
+                CREATE TABLE tasks_v28 (
+                    id TEXT PRIMARY KEY,
+                    title TEXT NOT NULL,
+                    description TEXT,
+                    status TEXT NOT NULL DEFAULT 'pending' CHECK (status IN ('pending','claimed','working','review','paused','escalated','waiting_human','done','failed','blocked','cancelled')),
+                    assignee TEXT,
+                    assigned_by TEXT,
+                    depends_on TEXT,
+                    parent_task TEXT,
+                    priority INTEGER NOT NULL DEFAULT 5,
+                    task_type TEXT,
+                    created_at TEXT NOT NULL DEFAULT (datetime('now')),
+                    updated_at TEXT NOT NULL DEFAULT (datetime('now')),
+                    claimed_at TEXT,
+                    started_at TEXT,
+                    completed_at TEXT,
+                    deadline TEXT,
+                    retry_count INTEGER NOT NULL DEFAULT 0,
+                    max_retries INTEGER NOT NULL DEFAULT 2,
+                    must_haves TEXT,
+                    risk_level TEXT DEFAULT 'standard',
+                    estimated_duration_minutes INTEGER,
+                    escalated INTEGER DEFAULT 0,
+                    current_agent TEXT,
+                    previous_agent TEXT,
+                    next_capability TEXT,
+                    stage TEXT,
+                    stages_json TEXT DEFAULT '[]',
+                    archived INTEGER DEFAULT 0,
+                    archived_at TEXT
+                );
+                INSERT INTO tasks_v28 SELECT * FROM tasks;
+                DROP TABLE tasks;
+                ALTER TABLE tasks_v28 RENAME TO tasks;
+            """)
+            # 重建索引
+            conn.executescript("""
+                CREATE INDEX IF NOT EXISTS idx_tasks_status ON tasks(status);
+                CREATE INDEX IF NOT EXISTS idx_tasks_assignee ON tasks(assignee);
+                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);
+            """)
+        finally:
+            if fk_was_on:
+                conn.execute("PRAGMA foreign_keys = ON")
 
     # 3. checkpoints 表（M3）
     conn.execute("""CREATE TABLE IF NOT EXISTS checkpoints (