Since this exercise was pseudo-code, I did not think particularly hard about the semantics of specific implementations, I just reasoned about what I would naively expect from any implementation. The answer I gave was the Trio answer - this was the first time I heard about Trio.

I realized I have very little experience with async/await; I've only used it extensively in Javascript and only in the browser there - so if my understanding of the exercise hinged on semantics of child_process.spawn then I had no reference point at all for that.

The languages that I have used extensively for back-end work either have native green-threads (Elixir, Haskell), or further back in my career I simply used synchronous I/O in Java and C# which only offered async or futures long after I'd moved on from them.

Frankly, this is a big part of why I chose Elixir and Haskell (and lately, some Go).

edit: Also thanks for your work on Zena, and mentioning it here! I've looked for exactly this before. Now I just have to invent a project for it :)