perf(web): release inactive mutation state

vehicle-data-platform/apps/web/src/v2/AppV2.cache.test.tsx

@@ -0,0 +1,26 @@
+import { QueryClientProvider, useMutation } from '@tanstack/react-query';
+import { cleanup, fireEvent, render, screen, waitFor } from '@testing-library/react';
+import { afterEach, expect, test } from 'vitest';
+import { createPlatformQueryClient } from './AppV2';
+
+afterEach(cleanup);
+
+test('keeps mutation feedback while mounted and releases completed writes after route unmount', async () => {
+  const client = createPlatformQueryClient();
+  const retainedPayload = { rows: Array.from({ length: 500 }, (_, index) => ({ vin: `VIN-${index}`, model: `MODEL-${index}` })) };
+
+  function MutationHarness() {
+    const mutation = useMutation({ mutationFn: async () => retainedPayload });
+    return <div><button type="button" onClick={() => mutation.mutate()}>执行写操作</button>{mutation.data ? <span>已处理 {mutation.data.rows.length} 行</span> : null}</div>;
+  }
+
+  const view = render(<QueryClientProvider client={client}><MutationHarness /></QueryClientProvider>);
+  fireEvent.click(screen.getByRole('button', { name: '执行写操作' }));
+
+  expect(await screen.findByText('已处理 500 行')).toBeInTheDocument();
+  expect(client.getMutationCache().getAll()).toHaveLength(1);
+
+  view.unmount();
+  await waitFor(() => expect(client.getMutationCache().getAll()).toHaveLength(0));
+  client.clear();
+});