{
  config,
  lib,
  pkgs,
  inputs,
  ...
}:
# The Skeleton's shared base config: the pieces every Host carries regardless of
# which Modules it enables — overlays, the `user`, flakes, and home-manager.
let
  inherit (lib) mkOption types;
  user = config.user;

  # Instantiate an extra nixpkgs source for the same platform as the base pkgs.
  pinArgs = prev: {
    inherit (prev.stdenv.hostPlatform) system;
    config.allowUnfree = true;
  };
in
{
  options.user = {
    name = mkOption {
      type = types.str;
      default = "alexion";
      description = ''
        The primary interactive user this Host is built for. Drives both the
        system account and the home-manager user in lockstep.
      '';
    };
    description = mkOption {
      type = types.str;
      default = "Alexion";
      description = "Human-readable description (GECOS field) for the primary user.";
    };
  };

  config = {
    # Base is nixos-unstable; reach a package fresher with `unstable.<name>` or
    # pin it rock-solid with `stable.<name>`. chaotic's overlay is added by its
    # own NixOS module, imported by the host-builder.
    nixpkgs.overlays = [
      (_final: prev: {
        unstable = import inputs.nixpkgs-unstable (pinArgs prev);
        stable = import inputs.nixpkgs-stable (pinArgs prev);
      })
    ];
    nixpkgs.config.allowUnfree = true;

    # Flakes + a baseline so `nixos-rebuild switch` works from the console.
    nix.settings.experimental-features = [
      "nix-command"
      "flakes"
    ];
    environment.systemPackages = [ pkgs.git ];

    # Primary user, in wheel. No password is set here.
    users.users.${user.name} = {
      isNormalUser = true;
      description = user.description;
      extraGroups = [ "wheel" ];
    };

    # home-manager as a NixOS module: one `nixos-rebuild switch` builds the
    # system and the user environment atomically, sharing the system's pkgs
    # (with our overlays) and installing user packages into the system profile.
    home-manager = {
      useGlobalPkgs = true;
      useUserPackages = true;
      extraSpecialArgs = {
        inherit inputs;
        my = inputs.self.lib;
      };
      users.${user.name} = {
        home.username = user.name;
        home.homeDirectory = "/home/${user.name}";
        home.stateVersion = "26.05";
      };
    };
  };
}