Vitest fake timers and microtasks

A production symptom appears first: flaky tests, stale state, slow UI, late cleanup, or growing memory. This reduces flaky Vitest/Jest tests around retries, debounce, polling, loaders, and React async state.

Expecting fake timers to prove every async assertion is ready.

Fix the root scheduling, cleanup, or concurrency pattern instead of adding arbitrary waits.

try {
  await operation();
} finally {
  cleanup();
}

The console lane proves the visible order: retry settled. The active line and queues show why source order changed.

Reproduce the symptom with a small test, apply the safer pattern, then verify the flaky, slow, or leaking behavior disappears.