That covers the one case in the example, but the language goes even further than that in ensuring constant-time processing of secrets, including ensuring speculative execution in the CPU won't expose the data to timing attacks.

I don't know enough about the subject to really evaluate this in detail, but I am more than willing to at least entertain the notion that the problem space is thorny enough that a language-level solution really can do some things that can't be as effectively accomplished with a library solution. Even in a language with a strong compiler like Rust.

Rune also has an interesting approach to pointer safety that's significantly different from Rust's: https://github.com/google/rune/blob/main/doc/index.md#runes-...