improve shelf hiearchy

shelf/default.nix

@@ -0,0 +1,24 @@
+{ pkgs, system }:
+let
+  denoShelf = import ./deno {
+    inherit pkgs system;
+    # collective hash of all (relevant) deno sources
+    # mapped to resulting shared deno cache hash
+    knownDenoHashes = {
+      "2JQI9Ie/fkl5Ltr22BGJynF9tFc=" =
+        "sha256-7csbrTbGd6J4a0Gkj9ndKhNxv90KeOHjr7DDNal3L4Q=";
+    };
+  };
+  
+  shelfSetup = pkgs.writeShellScript "setup-shelf" ''
+    export DENO_DIR=$PWD/.deno_cache
+    rm -rf $DENO_DIR
+    cp -r ${denoShelf.cache} $DENO_DIR
+    chmod -R u+w "$DENO_DIR"
+
+    # TODO: add other interpreters
+  '';
+in
+{
+  setupScript = shelfSetup;
+}