flake and design doc

flake.nix

@@ -0,0 +1,39 @@
+{
+  description = "Regolith, a retained mode GUI library in C";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+  };
+
+  outputs = { self, nixpkgs }:
+    let
+      systems = [ "x86_64-linux" "aarch64-linux" ];
+      forAllSystems = f: nixpkgs.lib.genAttrs systems (system:
+        f nixpkgs.legacyPackages.${system});
+    in {
+      devShells = forAllSystems (pkgs: {
+        default = pkgs.mkShell.override { stdenv = pkgs.clangStdenv; } {
+          nativeBuildInputs = with pkgs; [
+            cmake
+            ninja
+            pkg-config
+            clang-tools
+            emscripten
+            gdb
+            valgrind
+            lua5_4
+            lua-language-server
+          ];
+
+          buildInputs = with pkgs; [
+            sdl3
+            libGL
+          ];
+
+          shellHook = ''
+            export EM_CACHE="$PWD/.emscripten-cache"
+          '';
+        };
+      });
+    };
+}