{
  description = "Org-roam export pipeline — Elixir escript";

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

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs { inherit system; };
        fs = pkgs.lib.fileset;

        # Emacs with ox-hugo — needed at runtime by the pipeline escript
        # (export_org_files calls `emacs --batch` with ox-hugo).
        emacsWithOxHugo = (pkgs.emacsPackagesFor pkgs.emacs-nox).emacsWithPackages
          (epkgs: [ epkgs.ox-hugo ]);

        # Pre-fetched Hex/Mix dependencies.
        # src is filtered to mix.exs + mix.lock so source edits don't
        # invalidate this derivation.
        mixDeps = pkgs.beamPackages.fetchMixDeps {
          pname = "pipeline-mix-deps";
          version = "0.1.0";
          src = fs.toSource {
            root = ./.;
            fileset = fs.unions [
              ./mix.exs
              ./mix.lock
            ];
          };
          sha256 = "sha256-si7JAomY1HZ33m6ihUJP5i6PO39CE1clYvuMtn0CbPU=";
        };

        # Compiled pipeline escript (without runtime wrappers).
        pipelineEscript = pkgs.beamPackages.mixRelease {
          pname = "pipeline";
          version = "0.1.0";
          src = ./.;

          escriptBinName = "pipeline";
          mixFodDeps = mixDeps;

          stripDebug = true;
        };

        # Wrapped pipeline that puts emacs (with ox-hugo) on PATH so
        # the escript's System.cmd("emacs", ...) calls succeed.
        pipelineApp = pkgs.writeShellApplication {
          name = "pipeline";
          runtimeInputs = [ emacsWithOxHugo pkgs.inotify-tools ];
          text = ''
            exec ${pipelineEscript}/bin/pipeline "$@"
          '';
        };
      in
      {
        packages.default = pipelineApp;
        packages.escript = pipelineEscript;

        devShells.default = pkgs.mkShell {
          buildInputs = [
            pkgs.elixir
            pkgs.inotify-tools
            emacsWithOxHugo
          ];
        };
      });
}