Express slow route blocking

A production symptom appears first: flaky tests, stale state, slow UI, late cleanup, or growing memory. This affects PDF generation, image transforms, CSV exports, encryption, large JSON parsing, and analytics aggregation in Express/Fastify APIs.

Calling CPU-heavy synchronous work from latency-sensitive request handlers.

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: report sent -> health delayed. 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.