> thus it would be unsafe to continue execution of previously executing async functions.

There's more nuance than this. You can keep polling futures as often as you want. When an async fn gets converted into the state machine, yielding is just expressed as the poll fn returning as not ready.

So it is actually possible for "a little bit" of work to happen, although that's limited and gets tricky because the way wakers work ensure that normally futures only get polled by the runtime when there's actually work for them to do.