{
  description = "boxmaker: a sovereign personal agent harness";

  inputs = {
    nixpkgs.url = "nixpkgs/nixos-26.05";
    # The Rust toolchain, pinned below, independent of the host's nixpkgs release.
    rust-overlay = {
      url = "github:oxalica/rust-overlay";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs =
    {
      self,
      nixpkgs,
      rust-overlay,
    }:
    let
      systems = [ "x86_64-linux" ];
      forAllSystems = nixpkgs.lib.genAttrs systems;
      # nixpkgs with rust-overlay, and the one Rust toolchain every host uses (the workspace's
      # `rust-version`): cargo, rustc, clippy and rustfmt.
      pkgsFor =
        system:
        import nixpkgs {
          inherit system;
          overlays = [ rust-overlay.overlays.default ];
        };
      toolchainFor =
        pkgs:
        pkgs.rust-bin.stable."1.98.1".default.override {
          extensions = [
            "clippy"
            "rustfmt"
          ];
        };
      version =
        if self ? shortRev then
          self.shortRev
        else if self ? dirtyShortRev then
          self.dirtyShortRev
        else
          "dev";
    in
    {
      packages = forAllSystems (
        system:
        let
          pkgs = pkgsFor system;
          toolchain = toolchainFor pkgs;
          rustPlatform = pkgs.makeRustPlatform {
            cargo = toolchain;
            rustc = toolchain;
          };
          lib = pkgs.lib;
          # Only what the build reads: no target/, no .state/, no docs.
          src = lib.cleanSourceWith {
            src = ./.;
            filter =
              path: type:
              let
                rel = lib.removePrefix (toString ./. + "/") (toString path);
              in
              rel == "Cargo.toml" || rel == "Cargo.lock" || rel == "crates" || lib.hasPrefix "crates/" rel;
          };
          # Every binary of the workspace: the roles, bxctl and toolkit.
          boxmaker = rustPlatform.buildRustPackage {
            pname = "boxmaker";
            inherit version src;
            cargoLock.lockFile = ./Cargo.lock;
            # The tests run in `make gate`: they need Unix sockets under /tmp and scripts they write
            # and run, which the build sandbox is not checked to allow.
            doCheck = false;
            meta = {
              description = "a sovereign personal agent harness";
              mainProgram = "bxctl";
            };
          };
          # The image every tool container runs from; see the file for how it is loaded.
          tools-image = import ./deploy/tools-image.nix { inherit pkgs; };
        in
        {
          inherit boxmaker tools-image;
          default = boxmaker;
        }
      );

      devShells = forAllSystems (
        system:
        let
          pkgs = pkgsFor system;
        in
        {
          default = pkgs.mkShell {
            nativeBuildInputs = [
              (toolchainFor pkgs)
              pkgs.cargo-deny
              pkgs.gnumake
            ];
          };
        }
      );
    };
}