{
  description = "Personal agent skills, packaged through Nix.";

  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  inputs.flake-utils.url = "github:numtide/flake-utils";

  outputs =
    { self, nixpkgs, flake-utils }:
    let
      mkSkill = import ./lib/mk-skill.nix;
      discoverSkills = import ./lib/discover.nix nixpkgs.lib;

      discoveredSkills = discoverSkills ./skills;

      skillPackages =
        pkgs:
        nixpkgs.lib.listToAttrs (
          map (skill: {
            inherit (skill) name;
            value = mkSkill { inherit pkgs; inherit (skill) name src; };
          }) discoveredSkills
        );
    in
    {
      lib = { inherit mkSkill; };
    }
    //
    # An explicit system list rather than `eachDefaultSystem`.
    # That default set includes x86_64-darwin, which current nixpkgs no longer
    # evaluates (its `legacyPackages` throws).
    flake-utils.lib.eachSystem
      [
        "x86_64-linux"
        "aarch64-linux"
        "aarch64-darwin"
      ]
      (
        system:
        let
          pkgs = nixpkgs.legacyPackages.${system};
        in
        {
          # No `default`: a catalog has no single default skill.
          packages = skillPackages pkgs;

          # Each discovered skill is folded in as its own check, so
          # `nix flake check` builds every skill and fails on a malformed one.
          checks = (skillPackages pkgs) // {
            skill-build = import ./checks/skill-build.nix {
              inherit pkgs mkSkill discoverSkills;
            };
          };
        }
      );
}