Fair point. Though tbh I still think the user-isolation security for Linux is only really suited for the University/company threat model, where you generally trust users not to actually use exploits because they would get expelled/fired.
If you allow a completely untrusted user onto your system I think your chances of staying secure are low.
Then why rewrite coreutils in rust? TOCTOU isn't exact some new concept. Neither are https://owasp.org/Top10/2025/ (most of which a good web framework will prevent or migrate), and switching to rust (which as far as I know) won't bring you a safer web framework like django or rails.