fix(frontend): smooth realtime dashboard refreshes

app/game-frontend/src/utils/structuralShare.ts

@@ -0,0 +1,52 @@
+const isRecord = (value: unknown): value is Record<string, unknown> =>
+    value !== null && typeof value === 'object' && Object.getPrototypeOf(value) === Object.prototype;
+
+/**
+ * Reuses every unchanged branch from the current snapshot.
+ *
+ * tRPC returns a fresh object graph for every request. Assigning that graph
+ * directly makes Vue notify consumers even when their slice did not change.
+ * Structural sharing keeps that notification boundary aligned with actual
+ * value changes without maintaining a field-by-field event routing table.
+ */
+export const structurallyShare = <T>(current: T, incoming: T): T => {
+    if (Object.is(current, incoming)) {
+        return current;
+    }
+
+    if (current instanceof Date && incoming instanceof Date) {
+        return (current.getTime() === incoming.getTime() ? current : incoming) as T;
+    }
+
+    if (Array.isArray(current) && Array.isArray(incoming)) {
+        if (current.length !== incoming.length) {
+            return incoming;
+        }
+        let unchanged = true;
+        const shared = incoming.map((value, index) => {
+            const next = structurallyShare(current[index], value);
+            unchanged &&= Object.is(next, current[index]);
+            return next;
+        });
+        return (unchanged ? current : shared) as T;
+    }
+
+    if (isRecord(current) && isRecord(incoming)) {
+        const currentKeys = Object.keys(current);
+        const incomingKeys = Object.keys(incoming);
+        if (currentKeys.length !== incomingKeys.length || currentKeys.some((key) => !(key in incoming))) {
+            return incoming;
+        }
+
+        let unchanged = true;
+        const shared: Record<string, unknown> = {};
+        for (const key of incomingKeys) {
+            const next = structurallyShare(current[key], incoming[key]);
+            shared[key] = next;
+            unchanged &&= Object.is(next, current[key]);
+        }
+        return (unchanged ? current : shared) as T;
+    }
+
+    return incoming;
+};