{
  description = "agent-orchestrator — a generic multi-agent orchestration harness (tmux + watchdog)";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/50ab793786d9de88ee30ec4e4c24fb4236fc2674";
  };

  outputs = { self, nixpkgs }:
    let
      systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
      forAllSystems = f: nixpkgs.lib.genAttrs systems (system: f nixpkgs.legacyPackages.${system});
    in
    {
      # Reproducible devShell with the harness runtime deps. The driver itself is pure Python
      # stdlib (it needs tomllib, so python >= 3.11); the rest is what the agents/watchdog shell
      # out to. Make the agent CLIs (claude / opencode) available on PATH separately — they are
      # external, non-Nix tools; install them per their own docs, then `nix develop` here.
      devShells = forAllSystems (pkgs: {
        default = pkgs.mkShell {
          packages = [
            pkgs.python311   # stdlib tomllib (>=3.11) — the driver imports it
            pkgs.tmux        # every agent/session/watchdog runs in tmux
            pkgs.git         # handoff signalling watches origin/main
            pkgs.coreutils
            pkgs.bash
          ];
          shellHook = ''
            echo "agent-orchestrator devShell — $(python3 --version), $(tmux -V), $(git --version)"
            echo "try: python3 agents.py selftest  |  ./smoke.sh  |  python3 agents.py status --config agents.example.toml"
          '';
        };
      });

      # `nix flake check` evaluates this — a cheap smoke that the devShell builds.
      checks = forAllSystems (pkgs: {
        devshell-builds = self.devShells.${pkgs.system}.default;
      });
    };
}