is it not the case that in zig, the execution happens in a_future.await?

I presume that:

io.async 1 stores in io "hey please work on this"

io.async 2 stores in io "hey also please work on this"

in the case where io is evented with some "provided event loop":

await #1 runs through both 1 and 2 interleavedly, and if 2 finishes before 1, it puts a pin on it, and then returns a_result when 1 is completed.

await #2 "no-executions" if 1 finished after 2, but if there is still work to be done for 2, then it keeps going until the results for 2 are all in.

There's no "task that's running somewere mysteriously" unless you pick threaded io, in which case, yeah, io.async actually kicks shit off, and if the cpu takes a big fat nap on the calling thread between the asyncs and the awaits, progress might have been made (which wouldn't be the case if you were evented).