If you're deferring to another future, that's the first piece of the puzzle (which is primarily "solved" by having the compiler do some magic to make the deferr

If you're deferring to another future, that's the first piece of the puzzle (which is primarily "solved" by having the compiler do some magic to make the deferring easy, although things like the futures crate also provides a lot of useful interfaces for async I/O without actual implementations). At the end of the day, there is some fundamental future that has to implement the "schedule a call" piece, and that requires some degree of coordination with the top-level executor.