Edit the graph during play and watch values and flow run through it

The graph was only locked by five edit-mode guards in GraphCanvas. The
running game reads the graph by reference each frame, so a new node, edge,
changed value, disconnect or undo takes effect from the next frame. Stop
discards these edits like everything else changed in play. A new On start
node does not fire for a behavior that has already started.

During play every data output shows the value it last produced, in the
highlight colour and refreshed ten times a second. Values are kept per
graph, because node ids are only unique within one; with several
instances the most recent value wins. The Variables node reads the live
variable bag, so only its own outputs are kept, as a snapshot.

Each time an exec edge fires, a bead runs along it in 0.3 s, at most one
every 0.15 s per edge, following the same curve the edge is drawn with.
Beads run on game time and freeze while paused; the game logic is
unchanged.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/editor/graph/GraphEditor.ts

@@ -25,7 +25,7 @@ export class GraphEditor extends AssetTabEditor<BehaviorAsset, GraphCanvas> {
       this.breadcrumb,
     );
     this.canvas.onOpenBehavior = (id) => this.open(id, descend(this.trail, this.currentAssetId, id));
-    // Edits made while playing would be thrown away with the run.
+    // Play swaps in the runtime copy of the project, and back.
     state.on('mode', () => this.refresh());
   }
 
@@ -69,7 +69,6 @@ export class GraphEditor extends AssetTabEditor<BehaviorAsset, GraphCanvas> {
   }
 
   protected override syncExtras(asset: BehaviorAsset | null): void {
-    const editable = Boolean(asset) && this.state.mode === 'edit';
-    this.snapBox.setEnabled(editable);
+    this.snapBox.setEnabled(Boolean(asset));
   }
 }