Sync CPU-heavy work in request path

What it is

CPU-heavy synchronous work — image processing, PDF generation, encryption over a large payload, a big JSON parse — runs inside the request handler.

Why it matters

In a single-threaded runtime this blocks the event loop, so every other request on the instance waits behind it. One user's expensive operation becomes a latency spike for everyone sharing that process.

How to fix it

Move the work to a queue and return immediately with a job id, or push it to a worker thread or a separate service. If it must be inline, chunk it and yield between chunks so the loop can serve other requests.