add nix flake

.envrc

@@ -0,0 +1,3 @@
+# this caches nix setup, making day-to-day nix usage much faster.
+# see flake.nix for our nix setup
+use flake

.gitignore

@@ -9,3 +9,6 @@ yarn.lock
 .env
 dist
 lib
+
+# used by the nix when nix is used to provide a development environment
+.direnv

flake.nix

@@ -0,0 +1,36 @@
+# this flake installs all tools required for the dev env
+{
+  description = "nlx SDK dev env";
+
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+  inputs.nixpkgs.url = "github:nixos/nixpkgs/nixos-23.11";
+
+  outputs =
+    { self
+    , nixpkgs
+    , flake-utils
+    }:
+    flake-utils.lib.eachDefaultSystem (system:
+    let
+      assertVersion = version: pkg: (
+        assert (pkgs.lib.assertMsg (builtins.toString pkg.version == version) ''
+          Expecting version of ${pkg.name} to be ${version} but got ${pkg.version};
+        '');
+        pkg
+      );
+      pkgs = import nixpkgs
+        {
+          system = system;
+          config.allowUnfree = true;
+        };
+
+    in
+    {
+      formatter = pkgs.nixpkgs-fmt;
+      devShells.default = pkgs.mkShell {
+        packages = with pkgs; [
+          (assertVersion (nixpkgs.lib.strings.fileContents "${self}/.node-version") nodejs_18)
+        ];
+      };
+    });
+}