improve WebRTC NAT reliability diagnostics

server.js

@@ -24,6 +24,7 @@ const STATIC_DIR = fs.existsSync(path.join(__dirname, 'dist'))
 //   STUN_URLS           comma-separated stun: urls
 //   TURN_URLS           comma-separated turn:/turns: urls
 //   TURN_USERNAME / TURN_CREDENTIAL  static creds for all TURN urls
+//   ICE_TRANSPORT_POLICY optional WebRTC policy (all, relay, or none)
 //   TURN_LAN_HOST / TURN_LAN_SECRET  optional second, LAN-only TURN relay
 //                       (own coturn instance + secret, reachable only from
 //                       the local network via its own LoadBalancer IP with
@@ -85,7 +86,12 @@ function iceConfig() {
       });
     }
   }
-  return { iceServers };
+  const config = { iceServers };
+  const iceTransportPolicy = process.env.ICE_TRANSPORT_POLICY;
+  if (iceTransportPolicy && ['all', 'relay', 'none'].includes(iceTransportPolicy)) {
+    config.iceTransportPolicy = iceTransportPolicy;
+  }
+  return config;
 }
 
 // ---------------------------------------------------------------------------
@@ -323,4 +329,3 @@ if (require.main === module) {
 
 module.exports = { server, wss, iceConfig, allRoomsSnapshot, interval, startServer };
 
-