anchor.diff:    config = mkMerge [
       configuration
   
  -    (mkIf (! cfg.useDHCP) netConfig)
  -
       (mkIf cfg.docker.enable docker)
   
       (mkIf cfg.mailRelay.enable mailRelay)
  
positive.code: with lib;
  let
    cfg = config.features.os;
  
    netConfig = {
      networking.interfaces."${cfg.externalInterface}" = {
        useDHCP = false;
        ipv4.addresses = [ {
          address = cfg.address;
          prefixLength = 24;
        } ];
      };
    };
  
    configuration = {
      networking = {
  
negative.code:       description = "Boot disk (e.g. /dev/sda) for GRUB2";
      };
  
      externalInterface = mkOption {
        type = types.nullOr types.str;
        default = null;
        description = "External interface (i.e. for Docker nat)";
      };
  
      adminAuthorizedKeys = mkOption {
  