fix(canvas): defer store disposal until next store is ready — prevent tldraw reactive signals reading disposed store during async React unmount

src/pages/tldraw/singlePlayerPage.tsx

@@ -65,6 +65,7 @@ export default function SinglePlayerPage() {
         error: ''
     });
     const storeRef = useRef<TLStore | null>(null);
+    const prevStoreRef = useRef<TLStore | null>(null); // holds old store until tldraw has unmounted cleanly
     const [storeReady, setStoreReady] = useState(false);
 
     // TLDraw user preferences
@@ -139,6 +140,10 @@ export default function SinglePlayerPage() {
                     }, 2000);
                 });
 
+                // Dispose the previous store only AFTER we have a new one ready.
+                // Disposing while storeReady=true would crash tldraw's reactive signals.
+                prevStoreRef.current?.dispose();
+                prevStoreRef.current = null;
                 storeRef.current = newStore;
                 setStoreReady(true);
                 setCanvasPhase('ready');
@@ -154,8 +159,13 @@ export default function SinglePlayerPage() {
             snapshotServiceRef.current?.forceSaveCurrentNode().catch(() => {});
             snapshotServiceRef.current?.clearCurrentNode();
             snapshotServiceRef.current = null;
-            storeRef.current?.dispose();
-            storeRef.current = null;
+            // Don't dispose the store here — Tldraw is still subscribed via storeReady=true.
+            // Move the current store to prevStoreRef; it will be disposed when the next store is ready.
+            // This prevents tldraw's reactive signals from reading a disposed store during React's async unmount.
+            if (storeRef.current) {
+                prevStoreRef.current = storeRef.current;
+                storeRef.current = null;
+            }
             setStoreReady(false);
             setCanvasPhase('idle');
         };