feat: 优化 todo_write 工具的 merge 参数描述，调整默认值逻辑并添加测试

src/gateway/todo_prompt_provider.rs

@@ -27,8 +27,8 @@ const TODO_WRITE_INSTRUCTIONS: &str = r#"
 - 不需要为简单的单步操作（如回答一个问题、读取一个文件）创建 todo
 
 ### merge 参数
-- `merge: false`（默认）：全量替换 — 只传入需要追踪的 todo，不在列表中的项将被移除
+- `merge: true`（默认，推荐）：增量更新 — 只传入需要添加或更新的项，未提及的项保持不变。**绝大多数情况使用默认即可**
-- `merge: true`（推荐）：增量更新 — 只传入需要添加或更新的项，未提及的项保持不变。**绝大多数情况应该使用 merge=true**
+- `merge: false`：全量替换 — 只传入需要追踪的 todo，不在列表中的项将被移除
 
 ### 状态语义
 - `pending` — 尚未开始

src/protocol/ws_adapter.rs

@@ -26,6 +26,7 @@ pub(crate) fn ws_outbound_from_chat_message(message: &ChatMessage) -> Vec<WsOutb
                         topic_id: None,
                         timestamp: None,
                         reasoning_content: message.reasoning_content.clone(),
+                        user_message_id: None,
                     });
                 }
 
@@ -42,6 +43,7 @@ pub(crate) fn ws_outbound_from_chat_message(message: &ChatMessage) -> Vec<WsOutb
                     topic_id: None,
                     timestamp: None,
                     reasoning_content: tc_reasoning.clone(),
+                    user_message_id: None,
                 }));
                 outbound
             } else {
@@ -54,6 +56,7 @@ pub(crate) fn ws_outbound_from_chat_message(message: &ChatMessage) -> Vec<WsOutb
                     topic_id: None,
                     timestamp: None,
                     reasoning_content: message.reasoning_content.clone(),
+                    user_message_id: None,
                 }]
             }
         }

src/tools/todo_write.rs

@@ -77,9 +77,9 @@ impl Tool for TodoWriteTool {
 
     fn description(&self) -> &str {
         "Manage a structured task list for tracking work within the current conversation. \
-        Two modes: merge=false (default, full replacement — omitted items are removed); \
+        Two modes: merge=true (default, incremental — only send the items you want to add/update, \
-        merge=true (incremental — only send the items you want to add/update, \
+        previously existing items are preserved); \
-        previously existing items are preserved). \
+        merge=false (full replacement — omitted items are removed). \
         Use when you have 3+ distinct steps to track. \
         Rules: only ONE in_progress at a time, complete work before marking completed, \
         every item requires an id (generate a short random string for new items)."
@@ -91,7 +91,7 @@ impl Tool for TodoWriteTool {
             "properties": {
                 "merge": {
                     "type": "boolean",
-                    "description": "false (default): full replacement — todos not in the list are removed. true: incremental — only send items you want to add or update, existing items not mentioned are preserved."
+                    "description": "true (default): incremental — only send items you want to add or update, existing items not mentioned are preserved. false: full replacement — todos not in the list are removed."
                 },
                 "todos": {
                     "type": "array",
@@ -156,7 +156,7 @@ impl Tool for TodoWriteTool {
         let merge_mode = args
             .get("merge")
             .and_then(|v| v.as_bool())
-            .unwrap_or(false);
+            .unwrap_or(true);
 
         // 3. 读锁获取旧状态
         let old_items = {
@@ -754,11 +754,12 @@ mod tests {
             .await
             .unwrap();
 
-        // 只传入一个任务（任务B 被移除）
+        // 全量替换：只传入一个任务（任务B 被移除）
         let result = tool
             .execute_with_context(
                 &context,
                 json!({
+                    "merge": false,
                     "todos": [
                         {"id": "i1", "content": "任务A", "status": "in_progress"}
                     ]
@@ -1054,11 +1055,12 @@ mod tests {
             .await
             .unwrap();
 
-        // merge=false（默认）— 只传一个，另一个被删
+        // 显式指定 merge=false — 只传一个，另一个被删
         let result = tool
             .execute_with_context(
                 &context,
                 json!({
+                    "merge": false,
                     "todos": [
                         {"id": "p1", "content": "任务A", "status": "in_progress"}
                     ]
@@ -1140,4 +1142,45 @@ mod tests {
         assert!(!result.success);
         assert!(result.error.unwrap().contains("missing or empty 'id'"));
     }
+
+    #[tokio::test]
+    async fn test_default_is_merge_mode() {
+        let state = test_state();
+        let tool = TodoWriteTool::new(state.clone());
+        let context = test_context();
+
+        // 先创建 2 个 todo
+        let _ = tool
+            .execute_with_context(
+                &context,
+                json!({
+                    "todos": [
+                        {"id": "x1", "content": "任务A", "status": "pending"},
+                        {"id": "x2", "content": "任务B", "status": "pending"}
+                    ]
+                }),
+            )
+            .await
+            .unwrap();
+
+        // 不传 merge 参数，只更新一项 — 默认应为 merge=true，旧项保留
+        let result = tool
+            .execute_with_context(
+                &context,
+                json!({
+                    "todos": [
+                        {"id": "x1", "content": "任务A", "status": "in_progress"}
+                    ]
+                }),
+            )
+            .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(), 2); // 默认 merge，旧项保留
+        let task_a = todos.iter().find(|t| t["id"] == "x1").unwrap();
+        assert_eq!(task_a["status"], "in_progress");
+    }
 }

web/src/App.tsx

@@ -502,10 +502,10 @@ function App() {
       }
     }
 
-    // 过滤无实质内容的 merged_tool（无结果且非等待中）
+    // 过滤无实质内容的 merged_tool：result 到达后才显示保留；calling/pending 有 callContent 也保留
     return result.filter(msg => {
       if (msg.type !== 'merged_tool') return true
-      if (msg.status === 'pending') return true
+      if (msg.status === 'calling' || msg.status === 'pending') return true
       return !!(msg.resultContent && msg.resultContent.trim())
     })
   }, [messages])