[upstream #17164] useIsActiveItem spec flips back to false only after its assertion under load #385

client/src/hooks/__tests__/useIsActiveItem.spec.tsx fails intermittently under load in reviewctl precheck jest-client runs, and passes every time in isolation.

Failing test: useIsActiveItem > flips isActive back to false when data-active-item is removed

expect(received).toBe(expected) // Object.is equality
Expected: "false"
Received: "true"
  > 83 |     expect(probe.getAttribute('data-active')).toBe('false');

Seen on LibreChat-AI#17158 (twice), LibreChat-AI#17164 (jest-client shard 1/4, 2026-10-16) and LibreChat-AI#17030. None of these PRs touch the hook or its spec; npx jest src/hooks/__tests__/useIsActiveItem.spec.tsx passes 3/3 on the same heads.

Likely cause: the test awaits one MutationObserver delivery (nextActiveItemMutation) and then asserts synchronously, so under CPU contention the hook's state update from the removal can land after the assertion. A fix would wait for the attribute (waitFor) or flush the observer callback inside act before asserting.