[Arnavion]

You're probably thinking of IO streams that ultimately have their wakers woken via epoll - they do this by expecting there to be some IO reactor running the epoll loop that they can register their fd+waker with. They don't directly depend on a specific executor, just on the presence of a specific IO reactor. For something specific like tokio's IO streams, it would require tokio to provide its IO reactor as a standalone thing that could be run independent of using its `Runtime` executor.