Lily33

Does NOT delete any files that were written to, for example, ~/.local or ~/.config from dev shell.

One of OP’s problems was,

I’m making a mess of config files and extras.

Any files created by programs running in the dev environments will remain.

NixOS containers could do what OP’s asking for, but it’ll be trickier with just nix (on other distro). It’ll handle build dependencies and such, but you’ll still need to keep your home or other directories clean some other way.

NixOS does that well. I never quite managed to figure out a solution to this on other distros (which is actually what led me into making the jump in the end).