pxe/nixos

config.nix

{ config, pkgs, lib, ... }:

{
  #...
  services.pixiecore = let
    nixos = (import "${lib.cleanSource pkgs.path}/nixos/lib/eval-config.nix" {
      system = "x86_64-linux";
      modules = [ ./pxe.nix ];
    });
    build = nixos.config.system.build;
  in {
    enable = true;
    openFirewall = true;
    kernel = "${build.kernel}/bzImage";
    initrd = "${toString build.netbootRamdisk}/initrd";
    cmdLine = "init=.${build.toplevel}/init ${
        lib.concatStringsSep " " nixos.config.boot.kernelParams
      } boot.shell_on_fail";
    dhcpNoBind = true;
  };
  
  #...
  }

pxe.nix

{ lib, pkgs, config, modulesPath, ... }:

{
  services.getty.autologinUser = lib.mkForce "root";
  users.users.root.openssh.authorizedKeys.keys = [ config.sshkeys.pavel ];
  users.users.root.password = "nixos";
  boot.supportedFilesystems = [ "zfs" ];

  boot.kernelPackages = config.currentKernel;
  imports = [
    (modulesPath + "/installer/netboot/netboot.nix")
    (modulesPath + "/installer/cd-dvd/channel.nix")
    ../../shared-configs/consts.nix
    ../../shared-configs/generic/any.nix
  ];
  networking = {
    hostName = "nixtmp";
    hostId = "00000000";
  };

  nixpkgs = {
    overlays = [
      (self: super: {
        nix-quick-install = pkgs.callPackage
          "${config.localPkgs}/nix-quick-install/nix-quick-install.nix" { };
      })
    ];
  };

  hardware = {
    cpu.intel.updateMicrocode = true;
    cpu.amd.updateMicrocode = true;
    video.hidpi.enable = true;
  };

  environment.systemPackages = with pkgs; [ nix-quick-install ];

  system.stateVersion = config.systemStateVersion;
}

Seems like just

    nixos = inputs.nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules = [ ./pxe.nix ];
    };

fixes the issue

See also: https://github.com/gcoakes/nixboot/blob/master/flake.nix