Play switches to scene tab; graph tab strictly follows selection

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/editor/App.ts

@@ -256,6 +256,8 @@ class Editor {
     this.world.addSystem(this.behaviors);
     this.viewport.setWorld(this.world);
     this.state.setMode('play');
+    // Play always starts on the scene; the graph tab stays reachable for live tracing.
+    this.showTab('scene');
     this.state.setNotice(this.world.firstOfType('camera') ? 'Playing · Esc stops' : 'This scene has no camera – nothing is rendered · Esc stops');
     if (this.world.stopRequested) this.stop();
   }

src/editor/graph/GraphEditor.ts

@@ -20,8 +20,8 @@ interface PortAnchor {
 
 /**
  * The node graph editor for one behavior asset. Shows the graph of whatever behavior the
- * selection refers to (asset, placed object or node) and keeps showing it while unrelated
- * things are selected, so the user can flip between Scene and Graph tabs freely.
+ * selection refers to (asset, placed object or node). When nothing or a non-behavior is
+ * selected the editor is empty – the graph strictly mirrors the selection.
  *
  * Interactions: drag nodes, drag from port to port to connect, right-click the canvas for
  * the node palette, right-click a node or port for delete/disconnect, wheel to zoom, drag
@@ -100,7 +100,7 @@ export class GraphEditor extends Widget {
       this.sync();
       this.needsFit = true;
       this.fitView();
-    } else if (!this.asset()) {
+    } else if (!wanted || !this.asset()) {
       this.assetId = null;
       this.sync();
     } else {