feat(ui): 添加子 Agent 进度显示功能

当 build agent 调用 guide/explore 等子 agent 时，
用户可以在 web 页面实时看到子 agent 的执行进度

实现方案：
- Core: 使用 EventEmitter 模式发射子 agent 事件
- Server: 订阅事件并转发到 WebSocket
- UI: 处理事件并渲染 SubagentProgress 组件

新增文件：
- packages/core/src/agent/events.ts
- packages/ui/src/components/SubagentProgress.tsx

修改文件：
- core: executor.ts, manager.ts, types.ts, task.ts
- server: adapter.ts, types.ts
- ui: useChat.ts, types.ts
- web: Chat.tsx

packages/ui/src/hooks/useChat.ts

@@ -14,6 +14,13 @@ import type {
   MessagePart,
   ToolMessagePart,
   AgentModeType,
+  SubagentStartPayload,
+  SubagentEndPayload,
+  SubagentStreamPayload,
+  SubagentToolStartPayload,
+  SubagentToolEndPayload,
+  SubagentState,
+  SubagentToolInfo,
 } from '../api/types.js';
 
 interface UseChatOptions {
@@ -38,6 +45,8 @@ interface ChatState {
   autoApprove: boolean;
   /** 当前正在执行的 Agent 名称 */
   currentAgent: string;
+  /** 当前正在执行的子 Agent 状态 */
+  currentSubagent: SubagentState | null;
 }
 
 export function useChat({ sessionId, onError, onSessionNotFound, onSessionUpdated, onConfigError }: UseChatOptions) {
@@ -50,6 +59,7 @@ export function useChat({ sessionId, onError, onSessionNotFound, onSessionUpdate
     agentMode: 'build',
     autoApprove: false,
     currentAgent: 'build',
+    currentSubagent: null,
   });
 
   const wsRef = useRef<WebSocket | null>(null);
@@ -334,6 +344,122 @@ export function useChat({ sessionId, onError, onSessionNotFound, onSessionUpdate
               }));
             }
             break;
+
+          // ============ 子 Agent 事件处理 ============
+
+          case 'subagent:start': {
+            const payload = message.payload as SubagentStartPayload;
+            setState((prev) => ({
+              ...prev,
+              currentAgent: payload.agentName,
+              currentSubagent: {
+                id: payload.agentId,
+                name: payload.agentName,
+                description: payload.description,
+                status: 'running',
+                tools: [],
+                streamContent: '',
+              },
+            }));
+            break;
+          }
+
+          case 'subagent:tool_start': {
+            const payload = message.payload as SubagentToolStartPayload;
+            setState((prev) => {
+              if (!prev.currentSubagent || prev.currentSubagent.id !== payload.agentId) {
+                return prev;
+              }
+              const newTool: SubagentToolInfo = {
+                id: payload.toolCallId,
+                toolName: payload.toolName,
+                status: 'running',
+                args: payload.args,
+              };
+              return {
+                ...prev,
+                currentSubagent: {
+                  ...prev.currentSubagent,
+                  tools: [...prev.currentSubagent.tools, newTool],
+                },
+              };
+            });
+            break;
+          }
+
+          case 'subagent:stream': {
+            const payload = message.payload as SubagentStreamPayload;
+            setState((prev) => {
+              if (!prev.currentSubagent || prev.currentSubagent.id !== payload.agentId) {
+                return prev;
+              }
+              return {
+                ...prev,
+                currentSubagent: {
+                  ...prev.currentSubagent,
+                  streamContent: prev.currentSubagent.streamContent + payload.content,
+                },
+              };
+            });
+            break;
+          }
+
+          case 'subagent:tool_end': {
+            const payload = message.payload as SubagentToolEndPayload;
+            setState((prev) => {
+              if (!prev.currentSubagent || prev.currentSubagent.id !== payload.agentId) {
+                return prev;
+              }
+              const updatedTools = prev.currentSubagent.tools.map((tool) => {
+                if (tool.id === payload.toolCallId) {
+                  return {
+                    ...tool,
+                    status: payload.status === 'completed' ? 'completed' : 'error',
+                    result: payload.result,
+                    error: payload.error,
+                    duration: payload.duration,
+                  } as SubagentToolInfo;
+                }
+                return tool;
+              });
+              return {
+                ...prev,
+                currentSubagent: {
+                  ...prev.currentSubagent,
+                  tools: updatedTools,
+                },
+              };
+            });
+            break;
+          }
+
+          case 'subagent:end': {
+            const payload = message.payload as SubagentEndPayload;
+            setState((prev) => {
+              // 只有当 agentId 匹配时才处理
+              if (!prev.currentSubagent || prev.currentSubagent.id !== payload.agentId) {
+                return prev;
+              }
+              return {
+                ...prev,
+                currentAgent: prev.agentMode, // 恢复为主 Agent
+                currentSubagent: {
+                  ...prev.currentSubagent,
+                  status: payload.success ? 'completed' : 'error',
+                  duration: payload.duration,
+                  error: payload.error,
+                },
+              };
+            });
+            // 完成后短暂延迟再清除，让 UI 能显示最终状态
+            setTimeout(() => {
+              setState((prev) => ({
+                ...prev,
+                currentSubagent: null,
+              }));
+            }, 1000);
+            break;
+          }
         }
       } catch {
         // 忽略解析错误
@@ -476,6 +602,7 @@ export function useChat({ sessionId, onError, onSessionNotFound, onSessionUpdate
       agentMode: 'build',
       autoApprove: false,
       currentAgent: 'build',
+      currentSubagent: null,
     });
     reconnectAttemptsRef.current = 0;