fix: bidirectional streaming sync — phone→laptop now works

- Fix URL routing: /source/default and /stream/default paths
- _streamDiff sends via both source WS and receiver WS (INPUT flag)
- Source rebroadcasts 0x31 diffs from receivers to all other receivers
- Echo loop guard prevents infinite rebroadcast

compiler/ds-codegen/src/js_emitter.rs

@@ -1842,7 +1842,13 @@ const DS = (() => {
   function _initStream(url, mode) {
     _streamMode = mode || 'signal';
     _streamStart = performance.now();
-    _streamWs = new WebSocket(url);
+
+    // Ensure proper source path: ws://host:port → ws://host:port/source/default
+    var sourceUrl = url;
+    if (!url.match(/\/(source|stream)\//)) {
+      sourceUrl = url.replace(/\/?$/, '/source/default');
+    }
+    _streamWs = new WebSocket(sourceUrl);
     _streamWs.binaryType = 'arraybuffer';
     _streamWs.onmessage = function(e) {
       if (!(e.data instanceof ArrayBuffer) || e.data.byteLength < HEADER_SIZE) return;
@@ -1850,33 +1856,36 @@ const DS = (() => {
       var view = new DataView(bytes.buffer);
       var type = view.getUint8(0);
       var flags = view.getUint8(1);
+      // Source receives input from receivers (relay forwards receiver input to source)
       if (flags & 0x01) _handleRemoteInput(type, bytes.subarray(HEADER_SIZE));
     };
     _streamWs.onclose = function() { setTimeout(function() { _initStream(url, mode); }, 2000); };
-    console.log('[ds-stream] Source connected:', url, 'mode:', mode);
+    console.log('[ds-stream] Source connected:', sourceUrl);
 
     // Also open a receiver connection for bidirectional sync
-    var receiverUrl = url.replace(/\/source/, '/stream');
+    var receiverUrl = sourceUrl.replace('/source/', '/stream/');
     _initStreamReceiver(receiverUrl);
   }
 
-  // Receiver WS — listens for diffs from other clients via relay
+  var _recvWs = null;
+
+  // Receiver WS — listens for diffs from other sources via relay
   function _initStreamReceiver(url) {
-    var recvWs = new WebSocket(url);
+    _recvWs = new WebSocket(url);
-    recvWs.binaryType = 'arraybuffer';
+    _recvWs.binaryType = 'arraybuffer';
-    recvWs.onmessage = function(e) {
+    _recvWs.onmessage = function(e) {
       if (!(e.data instanceof ArrayBuffer) || e.data.byteLength < HEADER_SIZE) return;
       var bytes = new Uint8Array(e.data);
       var view = new DataView(bytes.buffer);
       var type = view.getUint8(0);
-      // Signal diff frame
+      // Signal diff from source — apply to local signals
       if (type === 0x31) {
         var payload = bytes.subarray(HEADER_SIZE);
         var json = new TextDecoder().decode(payload);
         _applyRemoteDiff(json);
       }
     };
-    recvWs.onclose = function() { setTimeout(function() { _initStreamReceiver(url); }, 2000); };
+    _recvWs.onclose = function() { setTimeout(function() { _initStreamReceiver(url); }, 2000); };
     console.log('[ds-stream] Receiver connected:', url);
   }
 
@@ -1895,11 +1904,28 @@ const DS = (() => {
   }
 
   function _streamDiff(name, value) {
-    if (!_streamWs || _streamMode !== 'signal') return;
+    if (_streamMode !== 'signal') return;
     if (_applyingRemoteDiff) return; // prevent echo loops
     var obj = {};
     obj[name] = (typeof value === 'object' && value !== null && 'value' in value) ? value.value : value;
-    _streamSend(0x31, 0, new TextEncoder().encode(JSON.stringify(obj)));
+    var payload = new TextEncoder().encode(JSON.stringify(obj));
+    // Send via source WS (broadcasts to all receivers)
+    if (_streamWs && _streamWs.readyState === 1) {
+      _streamSend(0x31, 0, payload);
+    }
+    // Also send via receiver WS with INPUT flag (relay forwards to source for rebroadcast)
+    if (_recvWs && _recvWs.readyState === 1) {
+      var ts = (performance.now() - _streamStart) | 0;
+      var msg = new Uint8Array(HEADER_SIZE + payload.length);
+      var v = new DataView(msg.buffer);
+      v.setUint8(0, 0x31);
+      v.setUint8(1, 0x01); // IS_INPUT flag
+      v.setUint16(2, (_streamSeq++) & 0xFFFF, true);
+      v.setUint32(4, ts, true);
+      v.setUint32(12, payload.length, true);
+      msg.set(payload, HEADER_SIZE);
+      _recvWs.send(msg.buffer);
+    }
   }
 
   function _streamSync(signals) {
@@ -1947,9 +1973,13 @@ const DS = (() => {
         emit('remote_scroll', { dx: view.getInt16(0, true), dy: view.getInt16(2, true) });
         break;
       case 0x31: {
-        // Signal diff — apply to local signals
+        // Signal diff from a receiver — apply locally AND rebroadcast to all receivers
         var json = new TextDecoder().decode(payload);
         _applyRemoteDiff(json);
+        // Rebroadcast via source WS so all other receivers get it
+        if (_streamWs && _streamWs.readyState === 1) {
+          _streamSend(0x31, 0, payload);
+        }
         break;
       }
     }