I'm also surprised how often the preemptive vs. cooperative angle gets ignored in favor of the stackful vs stackless debate.

If you choose a non-preemptive system, you naturally need yield points for cooperation. Those can either be explicit (await) or implicit (e.g. every function call). But you can get away with a minimal runtime and a stackless design.

Meanwhile, in a preemptive system you need a runtime that can interrupt other units of work. And it pushes you towards a stackful design.

All those decisions are downstream of the preemptive vs. cooperative.

In either case, you always need to be able to interface with CPU-heavy work. Either through preemption, or by isolating the CPU-heavy work.