The author is in the comfortable position of working on a system that does have a formal specification and a formally verified reference implementation. The post is not about how they wish things would work, but how their existing system (Cedar) works.

Regarding your point on Rust, the vast majority of software has nowhere near the amount of static guarantees provided by Rust. If you need more, use static memory allocation, that's what people do for safety critical systems. By the way, it seems that Rust aborts on OOM errors, not panics: https://github.com/rust-lang/rust/issues/43596