Enhance workflow engine and integration in backend and frontend

- Introduce a new WorkflowEngine class to manage workflow graphs, enabling dynamic node-based interactions.
- Update AssistantConfig to include a graph field for workflow definitions, allowing for flexible configuration.
- Modify pipeline execution to support workflow-driven dialogue, integrating node transitions and system prompts based on active nodes.
- Enhance frontend components to visualize active nodes and provide debugging capabilities, including highlighting the current node during interactions.
- Refactor existing components to accommodate new workflow functionalities and improve overall user experience.

frontend/src/hooks/use-voice-preview.ts

@@ -83,7 +83,10 @@ function microphoneErrorMessage(error: unknown): string {
   return errorMessage(error, "无法访问麦克风。");
 }
 
-export function useVoicePreview(assistantId: string | null) {
+export function useVoicePreview(
+  assistantId: string | null,
+  onNodeActive?: (nodeId: string | null) => void,
+) {
   const [status, setStatus] = useState<VoicePreviewStatus>("idle");
   const [error, setError] = useState<string | null>(null);
   const [micWarning, setMicWarning] = useState<string | null>(null);
@@ -102,6 +105,11 @@ export function useVoicePreview(assistantId: string | null) {
   const localStreamRef = useRef<MediaStream | null>(null);
   const startingRef = useRef(false);
   const messageSeqRef = useRef(0);
+  // 工作流激活节点回调存进 ref,避免把它挂进 connect 依赖反复重建连接
+  const onNodeActiveRef = useRef(onNodeActive);
+  useEffect(() => {
+    onNodeActiveRef.current = onNodeActive;
+  }, [onNodeActive]);
 
   // 枚举可用麦克风。未授权前 label 为空,授权(连接)后再刷新即可拿到名称。
   const refreshDevices = useCallback(async () => {
@@ -170,6 +178,7 @@ export function useVoicePreview(assistantId: string | null) {
     localStreamRef.current = null;
     if (audioRef.current) audioRef.current.srcObject = null;
     startingRef.current = false;
+    onNodeActiveRef.current?.(null);
   }, []);
 
   const disconnect = useCallback(() => {
@@ -377,6 +386,12 @@ export function useVoicePreview(assistantId: string | null) {
               sequence: messageSeqRef.current,
             };
             setMessages((prev) => sortMessages([...prev, next]));
+          } else if (
+            msg?.type === "node-active" &&
+            typeof msg.nodeId === "string"
+          ) {
+            // 工作流:后端报告当前激活节点,交给画布高亮
+            onNodeActiveRef.current?.(msg.nodeId);
           }
         } catch {
           /* 非 JSON / 未知消息,忽略 */