anchor.diff:  
       services.qemuGuest.enable = cfg.qemu.guestAgent.enable;
   
  -    system.build.vm = pkgs.runCommand "nixos-vm" {
  +    system.build.vm = cfg.host.pkgs.runCommand "nixos-vm" {
         preferLocalBuild = true;
         meta.mainProgram = "run-${config.system.name}-vm";
       }
         ''
           mkdir -p $out/bin
           ln -s ${config.system.build.toplevel} $out/system
  -        ln -s ${pkgs.writeScript "run-nixos-vm" startVM} $out/bin/run-${config.system.name}-vm
  +        ln -s ${cfg.host.pkgs.writeScript "run-nixos-vm" startVM} $out/bin/run-${config.system.name}-vm
         '';
   
       # When building a regular system configuration, override whatever
  
positive.code:         description = "Primary IP address used in /etc/hosts.";
        };
  
      virtualisation.qemu = {
        package =
          mkOption {
            type = types.package;
            default = pkgs.qemu_kvm;
            example = "pkgs.qemu_test";
            description = lib.mdDoc "QEMU package to use.";
          };
  
negative.code:   # Shell script to start the VM.
    startVM =
      ''
        #! ${cfg.host.pkgs.runtimeShell}
  
        export PATH=${makeBinPath [ cfg.host.pkgs.coreutils ]}''${PATH:+:}$PATH
  
        set -e
  
  