fix(frontend): smooth realtime dashboard refreshes

app/game-frontend/test/structuralShare.test.ts

@@ -0,0 +1,39 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { structurallyShare } from '../src/utils/structuralShare.ts';
+
+void test('reuses a completely unchanged tRPC snapshot', () => {
+    const current = {
+        general: { id: 7, name: '장수' },
+        records: [{ id: 3, text: '기록' }],
+        createdAt: new Date('2026-08-07T00:00:00.000Z'),
+    };
+    const incoming = {
+        general: { id: 7, name: '장수' },
+        records: [{ id: 3, text: '기록' }],
+        createdAt: new Date('2026-08-07T00:00:00.000Z'),
+    };
+
+    assert.equal(structurallyShare(current, incoming), current);
+});
+
+void test('replaces only changed branches and preserves sibling identities', () => {
+    const current = {
+        general: { id: 7, name: '이전 이름' },
+        city: { id: 1, name: '업' },
+        records: [{ id: 3, text: '기록' }],
+    };
+    const incoming = {
+        general: { id: 7, name: '새 이름' },
+        city: { id: 1, name: '업' },
+        records: [{ id: 3, text: '기록' }],
+    };
+
+    const shared = structurallyShare(current, incoming);
+    assert.notEqual(shared, current);
+    assert.notEqual(shared.general, current.general);
+    assert.deepEqual(shared.general, incoming.general);
+    assert.equal(shared.city, current.city);
+    assert.equal(shared.records, current.records);
+});