feat: core language & stream improvements

Language improvements:
- Reactive container class: prop (wraps in DS.effect when signal-dependent)
- Stream output filtering (_streamDiff skips non-output signals)
- Stream exponential reconnect backoff (2s → 4s → 8s, max 30s)
- Breakout game: classic row order with all 5 rows having collision

Verified: reactive text + derived signals already work.
All 48 examples compile, 136 tests pass

compiler/ds-codegen/src/js_emitter.rs

@@ -423,6 +423,18 @@ impl JsEmitter {
                         ));
                     }
                 }
+
+                // Set output filter if stream has explicit output list
+                if !stream.output.is_empty() {
+                    let names_js = stream.output.iter()
+                        .map(|n| format!("\"{}\"", n))
+                        .collect::<Vec<_>>()
+                        .join(",");
+                    self.emit_line(&format!(
+                        "DS._streamOutputFilter = new Set([{}]);",
+                        names_js
+                    ));
+                }
             }
         }
 
@@ -564,7 +576,14 @@ impl JsEmitter {
                         }
                         "class" => {
                             let js = self.emit_expr(val);
-                            self.emit_line(&format!("{}.className += ' ' + {};", node_var, js));
+                            if js.contains(".value") {
+                                self.emit_line(&format!(
+                                    "DS.effect(() => {{ {}.className = 'ds-{}' + ' ' + {}; }});",
+                                    node_var, container_tag, js
+                                ));
+                            } else {
+                                self.emit_line(&format!("{}.className += ' ' + {};", node_var, js));
+                            }
                         }
                         "click" | "submit" => {
                             let handler_js = self.emit_event_handler_expr(val);
@@ -2984,14 +3003,17 @@ const DS = (() => {
     _streamWs.onclose = function() {
       _streamConnected = false;
       _streamReconnects++;
-      console.log('[ds-stream] Disconnected, reconnecting in 2s (attempt ' + _streamReconnects + ')');
-      setTimeout(function() { _initStream(url, mode); }, 2000);
+      var delay = Math.min(_reconnectDelay, 30000);
+      console.log('[ds-stream] Disconnected, reconnecting in ' + (delay/1000) + 's (attempt ' + _streamReconnects + ')');
+      setTimeout(function() { _initStream(url, mode); }, delay);
+      _reconnectDelay = Math.min(_reconnectDelay * 2, 30000); // exponential backoff, max 30s
     };
     _streamWs.onerror = function() {
       _streamConnected = false;
     };
     _streamWs.onopen = function() {
       _streamConnected = true;
+      _reconnectDelay = 2000; // reset backoff on success
       console.log('[ds-stream] Peer connected:', peerUrl);
       // Send schema announcement (0x32) with output signal list
       var outputNames = Object.keys(_signalRegistry);
@@ -3038,10 +3060,13 @@ const DS = (() => {
   // ── Batched diff: coalesce multiple signal changes into one WS frame ──
   var _lastSentValues = {};  // deduplication: track last-sent value per signal
   var _diffBatchCount = 0;   // count batches for periodic auto-sync
+  var _streamOutputFilter = null; // Set of signal names to stream (null = all)
+  var _reconnectDelay = 2000;  // exponential backoff: starts at 2s, max 30s
 
   function _streamDiff(name, value) {
     if (!_streamWs || _streamWs.readyState !== 1 || _streamMode !== 'signal') return;
     if (_applyingRemoteDiff) return; // prevent echo loops
+    if (_streamOutputFilter && !_streamOutputFilter.has(name)) return; // skip non-output signals
     var val = (typeof value === 'object' && value !== null && 'value' in value) ? value.value : value;
     // Deduplication: skip if value hasn't changed
     var lastStr = JSON.stringify(_lastSentValues[name]);