os/modules/hm-system-defaults.nix

{ config, ... }:
{
  home-manager.sharedModules = [
    {
      home.sessionVariables = {
        inherit (config.environment.sessionVariables) NIX_PATH;
      };
      xdg.configFile."nix/registry.json".text = config.environment.etc."nix/registry.json".text;
    }
  ];
}