I actually think what the author is arguing is that async formalizes the idea of structuring your code to yield execution when it needs to "block". So block is

I actually think what the author is arguing is that async formalizes the idea of structuring your code to yield execution when it needs to "block". So block is leaky because it lacks a formal definition outside of an async annotated world. I find myself sympathetic to that take, despite my frustration with Rust's implementation of async, and the ecosystem/language shortcomings, etc.