This is a great question and there isn't a definitive answer provided in the sources I linked.

Broadly I think there are three approaches:

1. For frequent and small CPU heavy tasks, just run them on the IO threads. As long as you don't leave too long between `.await` points (~10ms) it seems to work okay.

2. Run your sans-io code on a dedicated CPU thread and do IO from an async runtime. This introduces overhead that needs to be weighed against the amount of CPU work.

3. Have the sans-io code output something like `Output::DoHeavyCompute { .. }` and later feed the result back as `Input::HeavyComputeResult { .. }`, in the middle run the work on a thread pool.