In reply to @wantguns:matrix.org
if there is an example flake i can follow which uses the output / config of a darwinConfiguration as colmena's host's options, that would help a lot

In your flake.nix on line 43 you have

nixpkgs = import nixpkgs { system = "x86_64-linux"; };

I'm suggesting you instead write

nixpkgs = import nixpkgs;

# ...
      deploy = {
        nodes = builtins.mapAttrs (name: hostConfig:
          let 
            isDarwin = hostConfig.platform == "darwin";
            activationPath = if isDarwin 
              then deploy-rs.lib.${hostConfig.system}.activate.darwin self.darwinConfigurations.${name}
              else deploy-rs.lib.${hostConfig.system}.activate.nixos self.nixosConfigurations.${name};
          in {
            hostname = hostConfig.hostname;
            profiles.system = {
              user = if isDarwin then hostConfig.username else "root";
              path = activationPath;
            };
          }
        ) hosts;
      };
# ...

I'm getting the following error on a simple deployment at the moment:

-> % colmena apply
[INFO ] Enumerating nodes...
error: infinite recursion encountered

       at /nix/store/y41rr1klzvwrmjs6smyl8kd1ipa5m5kj-source/lib/modules.nix:305:28:

          304|         builtins.addErrorContext (context name)
          305|           (args.${name} or config._module.args.${name})
             |                            ^
          306|       ) (lib.functionArgs f);
(use '--show-trace' to show detailed location information)
[ERROR] -----
[ERROR] Operation failed with error: Nix exited with error code: 1

NixOS config is

{ config, lib, pkgs, modulesPath, home-manager, ... }:
{
  deployment = {
    targetHost = "192.168.x.y";
    targetUser = "nixos";
    tags = [ "rpi" "lab" ];
  };

  imports = [
    (home-manager + "/nixos")
  ];
}