@unclechu @raboof yes that is precisely what i do now, and what this thread is about. it's also possible to add system packages without touching configuration.nix via `nix-env -i <pkg>` which then causes overlaps with the packages in configuration.nix, requiring an uninstall `nix-env --uninstall <pkg>` before `nixos-rebuild switch` will work.
@sneak @unclechu right - so you *can* get the behavior you want (by deciding not to use nix-env), but indeed you're not 'required' to.
I wonder if nix-env should even be installed on NixOS by default - I've always thought of it as something you'd use when using Nix outside of NixOS.