anchor.diff:        default = true;
         description = ''
           Whether the SD image should be compressed using
  -        <command>bzip2</command>.
  +        <command>zstd</command>.
         '';
       };
   
  
positive.code:     sdImage.storePaths = [ config.system.build.toplevel ];
  
      system.build.sdImage = pkgs.callPackage ({ stdenv, dosfstools, e2fsprogs,
      mtools, libfaketime, utillinux, bzip2, zstd }: stdenv.mkDerivation {
        name = config.sdImage.imageName;
  
        nativeBuildInputs = [ dosfstools e2fsprogs mtools libfaketime utillinux bzip2 zstd ];
  
        inherit (config.sdImage) compressImage;
  
  
negative.code: 
          echo "${pkgs.stdenv.buildPlatform.system}" > $out/nix-support/system
          if test -n "$compressImage"; then
            echo "file sd-image $img.zst" >> $out/nix-support/hydra-build-products
          else
            echo "file sd-image $img" >> $out/nix-support/hydra-build-products
          fi
  