兼容完成

Packages/com.unity.renderstreaming@3.1.0-exp.9/Runtime/Scripts/SignalingManagerInternal.cs

@@ -453,8 +453,17 @@ namespace Unity.RenderStreaming
                 pc = CreatePeerConnection(connectionId, e.polite);
             }
 
+            // 先触发 onGotOffer，让 Handler 在 SetRemoteDescription 之前添加 transceiver
+            // 这样 transceiver 会在 offer 的媒体行内正确匹配
+            onGotOffer?.Invoke(connectionId, e.sdp);
+
+            // 然后设置远程描述，完成后自动 SendAnswer
             RTCSessionDescription description = new RTCSessionDescription { type = RTCSdpType.Offer, sdp = e.sdp };
-            _startCoroutine(pc.OnGotDescription(description, () => onGotOffer?.Invoke(connectionId, e.sdp)));
+            _startCoroutine(pc.OnGotDescription(description, () =>
+            {
+                // SetRemoteDescription 成功后，自动创建并发送 answer
+                pc.SendAnswer();
+            }));
         }
 
         void OnParticipantJoinedHandler(ISignaling signaling, ParticipantEventData e)