todo

now:
- something is wrong with my age checks when nested nds
- all the checks now for age and lock and outdated could make it slow?
- nd refresh or something? you can `exec nd shell` if you want to get the updated env, can we make that easier, or more obvious? or warn?
    - exec nd shell might actually nest things, not really what we want
- nd build might not know flake authentication as in the flake alias we have?
- it doesnt point to symlinked and atomically switchable envs, its all directly into nix
- how to make a reusable tmux config for this?

later:
- two same `nd build` at the same time seems to build twice, nix doesnt make one wait?
- we start zsh, so bash functions are gone
    - but there are still a great many vars, some, like SHELL, is now wrong (not zsh)