feat(sfu): add mediasoup runtime and router capabilities endpoint

Backend/routes/streams.ts

@@ -503,6 +503,44 @@ router.get('/:streamSessionId/sfu/session', requireDeviceAuth, async (req, res)
   });
 });
 
+router.get('/:streamSessionId/sfu/router-rtp-capabilities', requireDeviceAuth, async (req, res) => {
+  const parsedParams = streamParamSchema.safeParse(req.params);
+  if (!parsedParams.success) {
+    res.status(400).json({ message: 'Invalid streamSessionId', errors: parsedParams.error.flatten() });
+    return;
+  }
+
+  const deviceAuth = ensureDeviceAuth(req, res);
+  if (!deviceAuth) return;
+
+  const sfu = ensureSfuEnabled(res);
+  if (!sfu) return;
+
+  const session = await getOwnedStreamSession(parsedParams.data.streamSessionId, deviceAuth.userId);
+  if (!session) {
+    res.status(404).json({ message: 'Stream session not found' });
+    return;
+  }
+
+  const isParticipant = session.requesterDeviceId === deviceAuth.deviceId || session.cameraDeviceId === deviceAuth.deviceId;
+  if (!isParticipant) {
+    res.status(403).json({ message: 'Device cannot access SFU router capabilities for this stream' });
+    return;
+  }
+
+  const routerRtpCapabilities = await sfu.getRouterRtpCapabilities(session.id);
+  if (!routerRtpCapabilities) {
+    res.status(409).json({ message: 'SFU session is not initialized for this stream' });
+    return;
+  }
+
+  res.json({
+    streamSessionId: session.id,
+    mediaMode,
+    routerRtpCapabilities,
+  });
+});
+
 router.post('/:streamSessionId/sfu/publish-transport', requireDeviceAuth, async (req, res) => {
   const parsedParams = streamParamSchema.safeParse(req.params);
   if (!parsedParams.success) {