diff --git a/src/gateway/tool_registry_factory.rs b/src/gateway/tool_registry_factory.rs
index cffaccc..9554f64 100644
--- a/src/gateway/tool_registry_factory.rs
+++ b/src/gateway/tool_registry_factory.rs
@@ -124,7 +124,7 @@ impl ToolRegistryFactory {
         }
         if self.is_enabled("todo_write") {
             if let Some(ref state) = self.todo_state {
-                registry.register(TodoWriteTool::new(state.clone()));
+                registry.register(TodoWriteTool::new(state.clone(), self.todo_repository.clone()));
                 registry.register(TodoReadTool::new(state.clone(), self.todo_repository.clone()));
             }
         }
@@ -232,7 +232,7 @@ impl ToolRegistryFactory {
         // Todo 追踪工具
         if self.is_enabled("todo_write") {
             if let Some(ref state) = self.todo_state {
-                registry.register(TodoWriteTool::new(state.clone()));
+                registry.register(TodoWriteTool::new(state.clone(), self.todo_repository.clone()));
                 registry.register(TodoReadTool::new(state.clone(), self.todo_repository.clone()));
             }
         }
diff --git a/src/tools/todo_write.rs b/src/tools/todo_write.rs
index d70a912..a9d7d49 100644
--- a/src/tools/todo_write.rs
+++ b/src/tools/todo_write.rs
@@ -6,6 +6,7 @@ use serde::Serialize;
 use serde_json::json;
 use tokio::sync::RwLock;
 
+use crate::storage::TodoRepository;
 use crate::tools::traits::{Tool, ToolContext, ToolResult};
 
 // ── 数据模型 ──────────────────────────────────────────────
@@ -61,11 +62,16 @@ pub struct TodoWriteTool {
     /// 内存状态：scope_key → Vec<TodoItem>
     /// scope_key = topic_id.unwrap_or(session_id)
     state: Arc<RwLock<HashMap<String, Vec<TodoItem>>>>,
+    /// 持久化仓库：内存为空时从 DB 回填，保证 merge 模式不丢失旧项
+    repository: Arc<dyn TodoRepository>,
 }
 
 impl TodoWriteTool {
-    pub(crate) fn new(state: Arc<RwLock<HashMap<String, Vec<TodoItem>>>>) -> Self {
-        Self { state }
+    pub(crate) fn new(
+        state: Arc<RwLock<HashMap<String, Vec<TodoItem>>>>,
+        repository: Arc<dyn TodoRepository>,
+    ) -> Self {
+        Self { state, repository }
     }
 }
 
@@ -158,10 +164,39 @@ impl Tool for TodoWriteTool {
             .and_then(|v| v.as_bool())
             .unwrap_or(true);
 
-        // 3. 读锁获取旧状态
+        // 3. 读锁获取旧状态；内存为空时从 DB 回填（与 TodoReadTool 一致，保证 merge 模式不丢失旧项）
         let old_items = {
             let guard = self.state.read().await;
-            guard.get(&scope_key).cloned().unwrap_or_default()
+            match guard.get(&scope_key).cloned() {
+                Some(items) if !items.is_empty() => items,
+                _ => {
+                    drop(guard);
+                    let db_items = match self.repository.list_todos(&scope_key) {
+                        Ok(records) if !records.is_empty() => {
+                            records
+                                .into_iter()
+                                .map(|r| TodoItem {
+                                    id: r.id,
+                                    content: r.content,
+                                    status: r.status,
+                                    created_by_message_id: r.created_by_message_id,
+                                })
+                                .collect::<Vec<_>>()
+                        }
+                        _ => Vec::new(),
+                    };
+                    if !db_items.is_empty() {
+                        let mut write_guard = self.state.write().await;
+                        write_guard.insert(scope_key.clone(), db_items.clone());
+                        tracing::info!(
+                            scope_key = %scope_key,
+                            todo_count = db_items.len(),
+                            "TodoWriteTool: backfilled memory from SQLite before merge"
+                        );
+                    }
+                    db_items
+                }
+            }
         };
 
         // 构建 id → TodoItem 的旧状态映射
@@ -444,9 +479,59 @@ mod tests {
         Arc::new(RwLock::new(HashMap::new()))
     }
 
+    struct MockTodoRepository {
+        records: Vec<crate::storage::TodoRecord>,
+    }
+
+    impl TodoRepository for MockTodoRepository {
+        fn replace_todos(
+            &self,
+            _scope_key: &str,
+            _items: &[crate::storage::TodoRecord],
+        ) -> Result<Vec<crate::storage::TodoRecord>, crate::storage::StorageError> {
+            Ok(vec![])
+        }
+
+        fn list_todos(
+            &self,
+            scope_key: &str,
+        ) -> Result<Vec<crate::storage::TodoRecord>, crate::storage::StorageError> {
+            Ok(self
+                .records
+                .iter()
+                .filter(|r| r.scope_key == scope_key)
+                .cloned()
+                .collect())
+        }
+    }
+
+    fn mock_repo() -> Arc<MockTodoRepository> {
+        Arc::new(MockTodoRepository { records: vec![] })
+    }
+
+    fn mock_record(
+        scope_key: &str,
+        id: &str,
+        content: &str,
+        status: &str,
+    ) -> crate::storage::TodoRecord {
+        crate::storage::TodoRecord {
+            id: id.to_string(),
+            scope_key: scope_key.to_string(),
+            session_id: "cli:chat-1".to_string(),
+            topic_id: None,
+            content: content.to_string(),
+            status: status.to_string(),
+            priority: "medium".to_string(),
+            created_at: 1000,
+            updated_at: 1000,
+            created_by_message_id: None,
+        }
+    }
+
     #[tokio::test]
     async fn test_create_initial_todos() {
-        let tool = TodoWriteTool::new(test_state());
+        let tool = TodoWriteTool::new(test_state(), mock_repo());
         let context = test_context();
 
         let result = tool
@@ -473,7 +558,7 @@ mod tests {
     #[tokio::test]
     async fn test_single_in_progress_constraint() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
         let context = test_context();
 
         let _ = tool
@@ -510,7 +595,7 @@ mod tests {
     #[tokio::test]
     async fn test_state_transition_in_progress_to_completed() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
         let context = test_context();
 
         let _ = tool
@@ -560,7 +645,7 @@ mod tests {
     #[tokio::test]
     async fn test_completed_can_revert_to_in_progress() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
         let context = test_context();
 
         // 创建并完成一个任务
@@ -609,7 +694,7 @@ mod tests {
     #[tokio::test]
     async fn test_cancelled_can_revert_to_pending() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
         let context = test_context();
 
         let _ = tool
@@ -657,7 +742,7 @@ mod tests {
     #[tokio::test]
     async fn test_in_progress_cannot_revert_to_pending() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
         let context = test_context();
 
         let _ = tool
@@ -703,7 +788,7 @@ mod tests {
 
     #[tokio::test]
     async fn test_new_item_can_be_any_status() {
-        let tool = TodoWriteTool::new(test_state());
+        let tool = TodoWriteTool::new(test_state(), mock_repo());
         let context = test_context();
 
         // 新项直接 completed — 应该允许（id 必填后不再限制初始状态）
@@ -724,7 +809,7 @@ mod tests {
 
     #[tokio::test]
     async fn test_new_item_can_start_as_in_progress() {
-        let tool = TodoWriteTool::new(test_state());
+        let tool = TodoWriteTool::new(test_state(), mock_repo());
         let context = test_context();
 
         let result = tool
@@ -751,7 +836,7 @@ mod tests {
     #[tokio::test]
     async fn test_remove_items_by_omission() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
         let context = test_context();
 
         let _ = tool
@@ -791,7 +876,7 @@ mod tests {
     #[tokio::test]
     async fn test_topic_isolation() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
 
         let main_context = ToolContext {
             session_id: Some("cli:chat-1".to_string()),
@@ -841,7 +926,7 @@ mod tests {
 
     #[tokio::test]
     async fn test_empty_list() {
-        let tool = TodoWriteTool::new(test_state());
+        let tool = TodoWriteTool::new(test_state(), mock_repo());
         let context = test_context();
 
         let result = tool
@@ -859,7 +944,7 @@ mod tests {
 
     #[tokio::test]
     async fn test_missing_todos_param() {
-        let tool = TodoWriteTool::new(test_state());
+        let tool = TodoWriteTool::new(test_state(), mock_repo());
         let context = test_context();
 
         let result = tool
@@ -873,7 +958,7 @@ mod tests {
 
     #[tokio::test]
     async fn test_no_context() {
-        let tool = TodoWriteTool::new(test_state());
+        let tool = TodoWriteTool::new(test_state(), mock_repo());
 
         let result = tool.execute(json!({})).await.unwrap();
 
@@ -884,7 +969,7 @@ mod tests {
     #[tokio::test]
     async fn test_subagent_isolation() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
 
         let parent_ctx = ToolContext {
             session_id: Some("cli:chat-1".to_string()),
@@ -935,7 +1020,7 @@ mod tests {
     #[tokio::test]
     async fn test_merge_mode_preserves_unreferenced_items() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
         let context = test_context();
 
         let _ = tool
@@ -977,7 +1062,7 @@ mod tests {
     #[tokio::test]
     async fn test_merge_mode_add_new_item() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
         let context = test_context();
 
         let _ = tool
@@ -1015,7 +1100,7 @@ mod tests {
     #[tokio::test]
     async fn test_merge_mode_never_removes() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
         let context = test_context();
 
         let _ = tool
@@ -1052,7 +1137,7 @@ mod tests {
     #[tokio::test]
     async fn test_non_merge_still_removes_by_omission() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
         let context = test_context();
 
         let _ = tool
@@ -1091,7 +1176,7 @@ mod tests {
     #[tokio::test]
     async fn test_merge_match_by_content_fallback() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
         let context = test_context();
 
         let _ = tool
@@ -1137,7 +1222,7 @@ mod tests {
 
     #[tokio::test]
     async fn test_missing_id_validation_error() {
-        let tool = TodoWriteTool::new(test_state());
+        let tool = TodoWriteTool::new(test_state(), mock_repo());
         let context = test_context();
 
         let result = tool
@@ -1159,7 +1244,7 @@ mod tests {
     #[tokio::test]
     async fn test_default_is_merge_mode() {
         let state = test_state();
-        let tool = TodoWriteTool::new(state.clone());
+        let tool = TodoWriteTool::new(state.clone(), mock_repo());
         let context = test_context();
 
         // 先创建 2 个 todo
@@ -1196,4 +1281,59 @@ mod tests {
         let task_a = todos.iter().find(|t| t["id"] == "x1").unwrap();
         assert_eq!(task_a["status"], "in_progress");
     }
+
+    #[tokio::test]
+    async fn test_merge_backfills_from_db_when_memory_empty() {
+        // 场景：进程重启后内存清空，DB 保留旧项 [a(completed), b(pending), c(in_progress)]
+        // 子智能体用 merge 模式只传 [{a, completed}]，应保留 b、c，不丢失
+        let state = test_state(); // 空 HashMap
+        let scope_key = "task:sub-1".to_string();
+        let repo = Arc::new(MockTodoRepository {
+            records: vec![
+                mock_record(&scope_key, "a", "任务A", "completed"),
+                mock_record(&scope_key, "b", "任务B", "pending"),
+                mock_record(&scope_key, "c", "任务C", "in_progress"),
+            ],
+        });
+        let tool = TodoWriteTool::new(state.clone(), repo);
+
+        let ctx = ToolContext {
+            session_id: Some("cli:chat-1".to_string()),
+            task_id: Some(scope_key.clone()),
+            nesting_depth: 1, // 模拟子智能体
+            ..ToolContext::default()
+        };
+
+        // merge=true 只传 a(completed)，b/c 应从 DB 回填并保留
+        let args = json!({
+            "merge": true,
+            "todos": [
+                { "id": "a", "content": "任务A", "status": "completed" }
+            ]
+        });
+
+        let result = tool.execute_with_context(&ctx, args).await.unwrap();
+        assert!(result.success, "merge should succeed: {:?}", result.error);
+
+        let output: serde_json::Value = serde_json::from_str(&result.output).unwrap();
+        let todos = output["current_todos"].as_array().unwrap();
+        assert_eq!(
+            todos.len(),
+            3,
+            "should preserve all 3 items after merge with DB backfill"
+        );
+
+        let ids: Vec<&str> = todos.iter().map(|t| t["id"].as_str().unwrap()).collect();
+        assert!(ids.contains(&"a"));
+        assert!(ids.contains(&"b"), "pending item b must be preserved");
+        assert!(
+            ids.contains(&"c"),
+            "in_progress item c must be preserved"
+        );
+
+        // 验证内存已被回填
+        let guard = state.read().await;
+        let memory_items = guard.get(&scope_key).unwrap();
+        assert_eq!(memory_items.len(), 3);
+    }
 }