{
  config,
  lib,
  pkgs,
  ...
}:
# The baseline interactive toolset as one deliberate bundle.
let
  cfg = config.modules.toolkit;
  user = config.user.name;
in
{
  options.modules.toolkit.enable =
    lib.mkEnableOption "the baseline interactive environment — fish, tmux, nvim, git, and direnv — as one unit";

  # Each piece is turned on at default priority, so a host can still override any one of them.
  config = lib.mkIf cfg.enable {
    home-manager.users.${user}.home.packages = with pkgs; [
      eza
      wget
    ];

    registry.shell-shortcut.${config.networking.hostName} = {
      ls = {
        command = "eza -alg --color=always --group-directories-first --icons=always";
        abbreviation = false;
      };
      la = {
        command = "eza -a --color=always --group-directories-first --icons=always";
        abbreviation = false;
      };
      ll = {
        command = "eza -lg --color=always --group-directories-first --icons=always";
        abbreviation = false;
      };
      lt = {
        command = "eza -aT -I '.git' --color=always --group-directories-first --icons=always";
        abbreviation = false;
      };
      "l." = {
        command = "eza -a | grep -e '^\\.'";
        abbreviation = false;
      };

      # Walk up the tree.
      ".." = "cd ..";
      "..." = "cd ../..";
      "...." = "cd ../../..";

      cp = "cp -v";
      tarnow = "tar -acf ";
      untar = "tar -zxvf ";
      wget = "wget -c ";
      grep = "grep --color=auto";
      fgrep = "fgrep --color=auto";
      egrep = "egrep --color=auto";
      jctl = "journalctl -p 3 -xb";

      # Rebuild the system, and reclaim disk from old generations.
      update = "sudo nixos-rebuild switch --flake .#${config.networking.hostName}";
      cleanup = "sudo nix-collect-garbage -d";
    };

    modules.fish.enable = lib.mkDefault true;
    # fish is also the login shell, so the bundled environment is what a shell drops into.
    modules.fish.defaultShell = lib.mkDefault true;
    modules.tmux.enable = lib.mkDefault true;
    modules.nvim.enable = lib.mkDefault true;
    modules.git.enable = lib.mkDefault true;
    modules.direnv.enable = lib.mkDefault true;
  };
}