{
  description = "My flake";

  inputs = {
    nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.1";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs =
    {
      self,
      nixpkgs,
      flake-utils,
    }:
    flake-utils.lib.eachDefaultSystem (
      system:
      let
        pkgs = import nixpkgs { inherit system; };
      in
      {
        bundlers = rec {
          proot-bundler =
            drv:
            pkgs.stdenvNoCC.mkDerivation {
              name = "myApp.run";
              nativeBuildInputs = [
                pkgs.nix
                pkgs.coreutils
                pkgs.findutils
                pkgs.gnutar
                pkgs.gzip
                pkgs.patchelf
              ];
              # patch proot as you described
              prootPatched = pkgs.proot.overrideAttrs (_: {
                postFixup = ''
                  exe=$out/bin/proot
                  ${pkgs.patchelf}/bin/patchelf \
                    --set-interpreter ."$(${pkgs.patchelf}/bin/patchelf --print-interpreter $exe)" \
                    --set-rpath "$(${pkgs.patchelf}/bin/patchelf --print-rpath $exe | sed 's|/nix/store/|./nix/store/|g')" \
                    $exe
                '';
              });

              buildCommand = ''
                set -euo pipefail
                # 1) Make payload dir that mirrors the bundle runtime layout
                PAY="$PWD/payload"
                mkdir -p "$PAY/nix/store"

                # include app + patched proot in the payload closure
                app=${drv}
                proot=${
                  self.bundlers.${system}.selfExtracting.prootPatched or ""
                } # not callable; we want the attr above
                proot=${
                  pkgs.proot.overrideAttrs (_: {
                    postFixup = "${pkgs.patchelf}/bin/patchelf --set-interpreter .\"$(${pkgs.patchelf}/bin/patchelf --print-interpreter $out/bin/proot)\" --set-rpath \"$( ${pkgs.patchelf}/bin/patchelf --print-rpath $out/bin/proot | sed 's|/nix/store/|./nix/store/|g')\" $out/bin/proot";
                  })
                }

                # copy closure of app + proot into ./nix/store
                paths=$( ${pkgs.nix}/bin/nix-store --query --requisites "$app" "$proot" )
                for p in $paths; do
                  cp -a --no-preserve=ownership "$p" "$PAY/nix/store/"
                done

                # discover targets for the launcher
                APP_BIN=$(find "$app/bin" -maxdepth 1 -type f -perm -111 | head -n1)
                APP_REL="/nix/store/$(basename "$(dirname "$APP_BIN")")/$(basename "$APP_BIN")"
                PROOT_REL="/nix/store/$(basename "$proot")/bin/proot"

                # 2) Tar.gz the payload
                ( cd "$PAY" && tar -czf "$PWD/payload.tar.gz" . )

                # 3) Assemble a self-extracting script at $out
                cat > $out <<'SH'
                #!/bin/sh
                set -euf
                # extract to temp dir
                : "''${TMPDIR:=/tmp}"
                EXTRACT_DIR="$(mktemp -d "''${TMPDIR%/}/nxbdl.XXXXXX")"
                cleanup() { [ -n "''${KEEP_BUNDLE:-}" ] || rm -rf "$EXTRACT_DIR"; }
                trap cleanup EXIT INT TERM

                # locate embedded archive (line after marker)
                ARCHIVE_LINE=$(awk '/^__ARCHIVE_BELOW__/ {print NR+1; exit 0}' "$0")
                tail -n +$ARCHIVE_LINE "$0" | tar -xzf - -C "$EXTRACT_DIR"

                cd "$EXTRACT_DIR"
                # vars substituted by bundler at build time:
                APP_REL='__APP_REL__'
                PROOT_REL='__PROOT_REL__'

                # run via proot
                BUNDLE_PWD="''${BUNDLE_PWD:-$PWD}"
                exec ".$PROOT_REL" \
                  -b ./nix:nix \
                  -R / \
                  -w "$BUNDLE_PWD" \
                  ".$APP_REL" "$@"

                __ARCHIVE_BELOW__
                SH

                # substitute the program + proot paths into the stub
                sed -i \
                  -e "s|__APP_REL__|$APP_REL|g" \
                  -e "s|__PROOT_REL__|$PROOT_REL|g" \
                  $out
                chmod +x $out

                # 4) Append the payload bytes after the marker
                cat payload.tar.gz >> $out
              '';
            };

          default = proot-bundler;
        };
      }
    );
}