To be clear, this bug was found running Nix on macOS, not iOS (just in case someone else besides me interpreted the two comments here as such).

Additional fun fact - the issue in question was not found during new development, but by just running the same code that had worked on previous macOS versions just fine. So besides a vulnerability, it's an user-visible regression to behaviour described by POSIX APIs.

I remember him beginning his work on Nix after his involvement in iPhone jailbreaking, but I might have not paid enough attention to the beginning of the Nix project.

Reminds me of when GreySyntax was trying to get Nginx to run on Linux as well. The reverse engineering / hacking community usually has all sorts of fun little goals to stretch tech past initial design.