fix: Report a go2rtc backchannel offer error as a failure rather than a missing capability (#2710)

src/components-lib/live/backchannel/go2rtc.ts

@@ -252,13 +252,11 @@ export class Go2RTCBackchannel implements Backchannel {
     message: Go2RTCMessage,
     generation: number,
   ): void {
-    // go2rtc refuses a stream it cannot send audio to with an error frame
-    // rather than an answer.
+    // The error frame go2rtc sends in place of an answer does not identify what
+    // failed, so the reason can be no more specific than `failed`, with the
+    // server's text attached as the description.
     if (isServerErrorForMode(message, 'webrtc')) {
-      this._failStart(
-        generation,
-        new BackchannelError('no_two_way_audio', message.value),
-      );
+      this._failStart(generation, new BackchannelError('failed', message.value));
       return;
     }
 

tests/components-lib/live/backchannel/go2rtc.test.ts

@@ -131,18 +131,21 @@ describe('Go2RTCBackchannel', () => {
       ).rejects.toMatchObject({ reason: 'failed', description: 'proxy' });
     });
 
-    it('should reject when the server reports the stream cannot take audio', async () => {
+    it('should reject with the server error when the offer is refused', async () => {
       const { backchannel, websocket } = setup();
       const started = backchannel.start(createStream().asMediaStream());
       await flushPromises();
       websocket.fireOpen();
       await flushPromises();
       websocket.fireMessage(
-        JSON.stringify({ type: 'error', value: 'webrtc: no backchannel' }),
+        JSON.stringify({
+          type: 'error',
+          value: 'webrtc/offer: streams: wrong response on DESCRIBE',
+        }),
       );
       await expect(started).rejects.toMatchObject({
-        reason: 'no_two_way_audio',
-        description: 'webrtc: no backchannel',
+        reason: 'failed',
+        description: 'webrtc/offer: streams: wrong response on DESCRIBE',
       });
     });