{
  description = "gleamtk — Gleam controller + Relm4 foreign node (Erlang distribution POC)";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  };

  outputs =
    { self, nixpkgs }:
    let
      systems = [
        "x86_64-linux"
        "aarch64-linux"
      ];
      forAllSystems = nixpkgs.lib.genAttrs systems;
    in
    {
      packages = forAllSystems (
        system:
        let
          pkgs = nixpkgs.legacyPackages.${system};
          gleamtk-ui = pkgs.rustPlatform.buildRustPackage {
            pname = "gleamtk-ui";
            version = "0.1.0";
            src = ./ui;
            cargoLock.lockFile = ./ui/Cargo.lock;

            nativeBuildInputs = with pkgs; [
              pkg-config
              wrapGAppsHook4
            ];

            buildInputs = with pkgs; [
              gtk4
              libadwaita
              adwaita-icon-theme
              hicolor-icon-theme
            ];

            meta = with pkgs.lib; {
              description = "Relm4 foreign node controlled by Gleam over Erlang distribution";
              license = licenses.mit;
              mainProgram = "gleamtk-ui";
              platforms = platforms.linux;
            };
          };
        in
        {
          inherit gleamtk-ui;
          default = gleamtk-ui;
        }
      );

      apps = forAllSystems (system: {
        default = {
          type = "app";
          program = "${self.packages.${system}.gleamtk-ui}/bin/gleamtk-ui";
        };
        ui = {
          type = "app";
          program = "${self.packages.${system}.gleamtk-ui}/bin/gleamtk-ui";
        };
      });

      devShells = forAllSystems (
        system:
        let
          pkgs = nixpkgs.legacyPackages.${system};
        in
        {
          default = pkgs.mkShell {
            name = "gleamtk";
            packages = with pkgs; [
              gleam
              beam.packages.erlang_27.erlang
              rebar3
              rustc
              cargo
              rustfmt
              clippy
              pkg-config
              gtk4
              libadwaita
              gsettings-desktop-schemas
              adwaita-icon-theme
              hicolor-icon-theme
              just
            ];

            # wrapGAppsHook rewrites packaged bins; bare `cargo run` still needs
            # schema/icon paths from the shell (see shellHook).
            nativeBuildInputs = with pkgs; [ wrapGAppsHook4 ];

            shellHook = ''
              export ERL_EPMD_ADDRESS=127.0.0.1
              export GSETTINGS_SCHEMAS_PATH="${pkgs.gtk4}/share/gsettings-schemas/${pkgs.gtk4.name}:${pkgs.gsettings-desktop-schemas}/share/gsettings-schemas/${pkgs.gsettings-desktop-schemas.name}:${pkgs.libadwaita}/share/gsettings-schemas/${pkgs.libadwaita.name}''${GSETTINGS_SCHEMAS_PATH:+:$GSETTINGS_SCHEMAS_PATH}"
              export XDG_DATA_DIRS="${pkgs.gsettings-desktop-schemas}/share:${pkgs.gtk4}/share:${pkgs.libadwaita}/share:${pkgs.adwaita-icon-theme}/share:${pkgs.hicolor-icon-theme}/share''${XDG_DATA_DIRS:+:$XDG_DATA_DIRS}"
              echo "gleamtk dev shell"
              echo "  just ui     # start Relm4 foreign node"
              echo "  just gleam  # start Gleam controller"
              echo "  just run    # ui in bg + gleam (needs display)"
              echo "  just smoke  # headless dist handshake test"
              echo "  nix build   # package gleamtk-ui"
            '';
          };
        }
      );

      formatter = forAllSystems (system: nixpkgs.legacyPackages.${system}.nixfmt-rfc-style);
    };
}