Refactor camera handling and video stream management in Assistant and MobileCall pages

- Remove direct camera start/stop calls and replace them with streamlined video stream handling.
- Update DebugVideoPanel to accept a streamOverride for better flexibility in video source management.
- Adjust MobileCallPage to utilize the new videoStream state, enhancing the call experience.
- Introduce videoStream state management in useVoicePreview for improved media handling during voice interactions.

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

@@ -89,6 +89,7 @@ export function useVoicePreview(
   const [error, setError] = useState<string | null>(null);
   const [micWarning, setMicWarning] = useState<string | null>(null);
   const [localStream, setLocalStream] = useState<MediaStream | null>(null);
+  const [videoStream, setVideoStream] = useState<MediaStream | null>(null);
   const [remoteStream, setRemoteStream] = useState<MediaStream | null>(null);
   const [messages, setMessages] = useState<ChatMessage[]>([]);
   const [callEnded, setCallEnded] = useState(false);
@@ -161,6 +162,7 @@ export function useVoicePreview(
   const disconnect = useCallback(() => {
     releaseResources();
     setLocalStream(null);
+    setVideoStream(null);
     setRemoteStream(null);
     setMessages([]);
     messageSeqRef.current = 0;
@@ -173,6 +175,7 @@ export function useVoicePreview(
   const fail = useCallback((message: string) => {
     releaseResources();
     setLocalStream(null);
+    setVideoStream(null);
     setRemoteStream(null);
     setError(message);
     setNetworkQuality("unknown");
@@ -306,6 +309,10 @@ export function useVoicePreview(
       onDeviceError: (deviceError) => {
         setMicWarning(deviceError.message || "无法访问麦克风。已尝试继续连接。");
       },
+      onCamUpdated: () => {
+        const track = transport.tracks().local.video;
+        setVideoStream(track ? new MediaStream([track]) : null);
+      },
       onTransportStateChanged: (nextState) => {
         if (nextState === "connected" || nextState === "ready") {
           setStatus("connected");
@@ -331,7 +338,9 @@ export function useVoicePreview(
         await transport.updateMic(selectedDeviceIdRef.current);
       }
       const localAudio = transport.tracks().local.audio;
+      const localVideo = transport.tracks().local.video;
       setLocalStream(localAudio ? new MediaStream([localAudio]) : null);
+      setVideoStream(localVideo ? new MediaStream([localVideo]) : null);
       void refreshDevices();
 
       const request = new Request(`${API_BASE}/api/webrtc/offer`, {
@@ -377,6 +386,10 @@ export function useVoicePreview(
     if (transport && deviceId) await transport.updateCam(deviceId);
   }, []);
 
+  const selectCamera = useCallback((deviceId: string) => {
+    transportRef.current?.updateCam(deviceId);
+  }, []);
+
   const selectDevice = useCallback(async (deviceId: string) => {
     setSelectedDeviceId(deviceId);
     selectedDeviceIdRef.current = deviceId;
@@ -413,6 +426,7 @@ export function useVoicePreview(
     error,
     micWarning,
     localStream,
+    videoStream,
     remoteStream,
     messages,
     callEnded,
@@ -428,6 +442,7 @@ export function useVoicePreview(
     sendText,
     connect,
     replaceVideoStream,
+    selectCamera,
     disconnect,
     audioRef,
   };