another one

system/nix/default.nix

@@ -0,0 +1,44 @@
+{
+  inputs,
+  lib,
+  config,
+  pkgs,
+  ...
+}: {
+  imports = [
+    ./nixpkgs
+    ./home-manager
+    ./substituters
+  ];
+
+  environment = {
+    systemPackages = [
+      pkgs.git
+      pkgs.scx
+      pkgs.stow
+    ];
+    localBinInPath = true;
+  };
+
+  nix = {
+    # pin the registry to avoid downloading and evaling a new nixpkgs version every time
+    registry = lib.mapAttrs (_: v: {flake = v;}) inputs;
+
+    # set the path for channels compat
+    nixPath = lib.mapAttrsToList (key: _: "${key}=flake:${key}") config.nix.registry;
+
+    settings = {
+      auto-optimise-store = true;
+      builders-use-substitutes = true;
+      warn-dirty = false;
+      experimental-features = ["nix-command" "flakes"];
+      flake-registry = "/etc/nix/registry.json";
+
+      # for direnv GC roots
+      keep-derivations = true;
+      keep-outputs = true;
+
+      trusted-users = ["root" "@wheel"];
+    };
+  };
+}