{
  description = "THROWAWAY Wayfinder #6 Dovecot/FUSE prototype";

  inputs = {
    nixpkgs23.url = "github:NixOS/nixpkgs/nixos-24.05";
    nixpkgs24.url = "github:NixOS/nixpkgs/nixos-unstable";
  };

  outputs = { self, nixpkgs23, nixpkgs24 }:
    let
      linuxSystems = [ "x86_64-linux" "aarch64-linux" ];
      forLinuxSystems = nixpkgs24.lib.genAttrs linuxSystems;
      makePackage = pkgs: pkgs.rustPlatform.buildRustPackage {
        pname = "wayfinder-6-prototype";
        version = "0.0.0";
        src = ./prototype/wayfinder-6;
        cargoLock.lockFile = ./prototype/wayfinder-6/Cargo.lock;
        doCheck = true;
      };
      packagesFor = system:
        let
          pkgs23 = import nixpkgs23 { inherit system; };
          pkgs24 = import nixpkgs24 { inherit system; };
        in {
          inherit pkgs23 pkgs24;
          # fuser 0.17 uses edition 2024; build both prototype binaries with
          # current Rust while testing each binary against its Dovecot generation.
          package23 = makePackage pkgs24;
          package24 = makePackage pkgs24;
        };
      vmTest = pkgs: package: generation: separator:
        import ./prototype/wayfinder-6/nix/vm-test.nix {
          inherit pkgs package generation separator;
          dovecot = pkgs.dovecot;
        };
      checksFor = system:
        let built = packagesFor system;
        in {
          dovecot-2_3-dot = vmTest built.pkgs23 built.package23 "2.3" ".";
          dovecot-2_3-slash = vmTest built.pkgs23 built.package23 "2.3" "/";
          dovecot-2_4-dot = vmTest built.pkgs24 built.package24 "2.4" ".";
          dovecot-2_4-slash = vmTest built.pkgs24 built.package24 "2.4" "/";
        };
      runnerFor = runnerPkgs: targetSystem: runnerPkgs.writeShellApplication {
        name = "wayfinder-6-vm-test-${targetSystem}";
        text = ''
          set -x
          nix build -L \
            ${self}#checks.${targetSystem}.dovecot-2_3-dot \
            ${self}#checks.${targetSystem}.dovecot-2_3-slash \
            ${self}#checks.${targetSystem}.dovecot-2_4-dot \
            ${self}#checks.${targetSystem}.dovecot-2_4-slash
        '';
      };
      appFor = runnerPkgs: targetSystem: {
        type = "app";
        program = "${runnerFor runnerPkgs targetSystem}/bin/wayfinder-6-vm-test-${targetSystem}";
      };
      darwinPkgs = import nixpkgs24 { system = "aarch64-darwin"; };
      darwinAarch64App = appFor darwinPkgs "aarch64-linux";
    in {
      packages = forLinuxSystems (system: {
        default = (packagesFor system).package24;
      });
      checks = forLinuxSystems checksFor;
      apps = (forLinuxSystems (system: {
        default = appFor (packagesFor system).pkgs24 system;
        vm-test = appFor (packagesFor system).pkgs24 system;
      })) // {
        # Run these from Apple Silicon with a matching Colima builder for aarch64,
        # or an x86_64-linux QEMU/TCG builder for the cross-architecture matrix.
        aarch64-darwin = {
          default = darwinAarch64App;
          vm-test-aarch64-linux = darwinAarch64App;
          vm-test-x86_64-linux = appFor darwinPkgs "x86_64-linux";
        };
      };
    };
}