fix: merge 模式下按 content 匹配已有项，无需 agent 记住 UUID

- merge=true 时，无 id 的项先按 content 匹配已有项
- 匹配到→更新，匹配不到→新建（仍需 pending/in_progress）
- 新增 list_todos 命令处理器，支持前端自动拉取
- prompt 增加规则6：更新已有任务必须传 id（作为最佳实践提示）

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/tools/todo_write.rs

@@ -272,7 +272,31 @@ impl Tool for TodoWriteTool {
                         updated_at: now,
                     });
                 } else {
-                    // 传入 id 但旧状态中没有 → 按新 item 处理
+                    // 传入 id 但旧状态中没有 → merge 模式按 content 匹配，否则按新 item
+                    if merge_mode {
+                        if let Some(old_item) = old_items.iter().find(|oi| oi.content == content) {
+                            let old_status = match TodoStatus::from_str(&old_item.status) {
+                                Some(s) => s,
+                                None => {
+                                    validation_errors.push(format!("Item '{}': corrupted old status", content));
+                                    continue;
+                                }
+                            };
+                            if let Err(err) = validate_transition(&old_status, &new_status) {
+                                validation_errors.push(format!("Item '{}': {}", content, err));
+                                continue;
+                            }
+                            processed_items.push(TodoItem {
+                                id: old_item.id.clone(),
+                                content,
+                                status: new_status.as_str().to_string(),
+                                priority: priority.as_str().to_string(),
+                                created_at: old_item.created_at,
+                                updated_at: now,
+                            });
+                            continue;
+                        }
+                    }
                     if !is_valid_new_status(&new_status) {
                         validation_errors.push(format!(
                             "Item '{}': new items must start as 'pending' or 'in_progress', got '{}'",
@@ -280,7 +304,6 @@ impl Tool for TodoWriteTool {
                         ));
                         continue;
                     }
-
                     processed_items.push(TodoItem {
                         id: id.to_string(),
                         content,
@@ -291,7 +314,31 @@ impl Tool for TodoWriteTool {
                     });
                 }
             } else {
-                // 新 item（无 id）— 允许 pending 或 in_progress
+                // 新 item（无 id）— merge 模式按 content 匹配，否则按新 item
+                if merge_mode {
+                    if let Some(old_item) = old_items.iter().find(|oi| oi.content == content) {
+                        let old_status = match TodoStatus::from_str(&old_item.status) {
+                            Some(s) => s,
+                            None => {
+                                validation_errors.push(format!("Item '{}': corrupted old status", content));
+                                continue;
+                            }
+                        };
+                        if let Err(err) = validate_transition(&old_status, &new_status) {
+                            validation_errors.push(format!("Item '{}': {}", content, err));
+                            continue;
+                        }
+                        processed_items.push(TodoItem {
+                            id: old_item.id.clone(),
+                            content,
+                            status: new_status.as_str().to_string(),
+                            priority: priority.as_str().to_string(),
+                            created_at: old_item.created_at,
+                            updated_at: now,
+                        });
+                        continue;
+                    }
+                }
                 if !is_valid_new_status(&new_status) {
                     validation_errors.push(format!(
                         "Item '{}': new items must start as 'pending' or 'in_progress', got '{}'",
@@ -299,7 +346,6 @@ impl Tool for TodoWriteTool {
                     ));
                     continue;
                 }
-
                 processed_items.push(TodoItem {
                     id: uuid::Uuid::new_v4().to_string(),
                     content,
@@ -1197,4 +1243,52 @@ mod tests {
         assert_eq!(todos.len(), 1);
         assert_eq!(output["changes"]["removed"].as_array().unwrap().len(), 1);
     }
+
+    #[tokio::test]
+    async fn test_merge_match_by_content_without_id() {
+        let state = test_state();
+        let tool = TodoWriteTool::new(state.clone());
+        let context = test_context();
+
+        // 先创建 3 个 pending 任务
+        let _ = tool
+            .execute_with_context(
+                &context,
+                json!({
+                    "todos": [
+                        {"content": "任务1", "status": "pending"},
+                        {"content": "任务2", "status": "pending"},
+                        {"content": "任务3", "status": "pending"}
+                    ]
+                }),
+            )
+            .await
+            .unwrap();
+
+        // merge: true — 直接传 content + completed，不传 id，按 content 匹配
+        let result = tool
+            .execute_with_context(
+                &context,
+                json!({
+                    "merge": true,
+                    "todos": [
+                        {"content": "任务1", "status": "completed"},
+                        {"content": "任务2", "status": "completed"},
+                        {"content": "任务3", "status": "cancelled"}
+                    ]
+                }),
+            )
+            .await
+            .unwrap();
+
+        assert!(result.success);
+        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);
+        assert_eq!(todos.iter().find(|t| t["content"] == "任务1").unwrap()["status"], "completed");
+        assert_eq!(todos.iter().find(|t| t["content"] == "任务2").unwrap()["status"], "completed");
+        assert_eq!(todos.iter().find(|t| t["content"] == "任务3").unwrap()["status"], "cancelled");
+        assert_eq!(output["changes"]["updated"].as_array().unwrap().len(), 3);
+        assert_eq!(output["changes"]["added"].as_array().unwrap().len(), 0);
+    }
 }