add nixos wrapper

infra/common/nixos/wrapper.nix

@@ -0,0 +1,27 @@
+{
+  system,
+  configuration,
+}:
+let
+  sources = import ../../../npins;
+  os = import "${sources.nixpkgs}/nixos" {
+    # os = import <nixpkgs/nixos> {
+    inherit system configuration;
+    # system = "${local.system}";
+    # configuration =
+    #   ${var.config_nix} //
+    #   # template parameters passed in from TF thru json
+    #   builtins.fromJSON "${replace(jsonencode(var.config_tf), "\"", "\\\"")}" //
+    #   {
+    #     # nix path for debugging
+    #     nix.nixPath = [ "${local.nix_path}" ];
+    #   };
+  };
+in
+# info we want to get back out
+{
+  substituters = builtins.concatStringsSep " " os.config.nix.settings.substituters;
+  trusted_public_keys = builtins.concatStringsSep " " os.config.nix.settings.trusted-public-keys;
+  drv_path = os.config.system.build.toplevel.drvPath;
+  out_path = os.config.system.build.toplevel;
+}