i don't have experience with rust async, although i used to maintain a csp protocol stack in python async, which is pretty similar, so tell me if this is wrong

i feel like the same kind of thing can happen even if you start entirely async, because something that was previously synchronous may have to become asynchronous, which leads to having to revalidate all your concurrency assumptions all the way up its (static) call stack. wherever you were depending on not getting preempted, you need to change the code to not depend on that anymore. but if ram is so tight that you're concerned about the sram for a second stack, maybe that's a pretty small task rather than a major rewrite

that said, i don't recall having actually had that problem