Fix datachannel handling: auto-create channels from remote peer

Modified peerDataChannelHandler to automatically create DurableChannel
instances when receiving data channels from the remote peer. This fixes
the connection flow where the answerer needs to receive the data channel
that the offerer created.

Previously, the handler only attached if a DurableChannel already existed,
which meant incoming channels from the remote peer would be ignored.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/durable/connection.ts

@@ -324,11 +324,20 @@ export class DurableConnection extends EventEmitter<DurableConnectionEvents> {
     };
 
     this.peerDataChannelHandler = (channel: RTCDataChannel) => {
-      // Find matching durable channel and attach
-      const durableChannel = this.channels.get(channel.label);
-      if (durableChannel) {
-        durableChannel.attachToChannel(channel);
+      // Find or create durable channel
+      let durableChannel = this.channels.get(channel.label);
+
+      if (!durableChannel) {
+        // Auto-create channel for incoming data channels
+        durableChannel = new DurableChannel(channel.label, {
+          maxQueueSize: this.config.maxQueueSize,
+          maxMessageAge: this.config.maxMessageAge
+        });
+        this.channels.set(channel.label, durableChannel);
       }
+
+      // Attach the received channel
+      durableChannel.attachToChannel(channel);
     };
 
     peer.on('connected', this.peerConnectedHandler);