monorepo lab stuff, init zen

nixos/modules/nix.nix

@@ -0,0 +1,46 @@
+{ host, pkgs, config, lib, ...}:
+let cfg = config.system-nix; in {
+  options.system-nix = {
+    enable = lib.mkOption {
+      type = lib.types.bool;
+      default = true;
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    programs = {
+      nix-index = {
+        enableBashIntegration = false;
+        enableZshIntegration = false;
+      };
+      nix-index-database.comma.enable = true;
+    };
+    nix = {
+      package = pkgs.nixVersions.nix_2_31; # https://github.com/serokell/deploy-rs/issues/340
+      settings = {
+        auto-optimise-store = true;
+        substituters = [
+          "https://install.determinate.systems"
+          "https://nvim-treesitter-main.cachix.org"
+        ];
+        trusted-public-keys = [
+          "cache.flakehub.com-3:hJuILl5sVK4iKm86JzgdXW12Y2Hwd5G07qKtHTOcDCM="
+          "nvim-treesitter-main.cachix.org-1:cbwE6blfW5+BkXXyeAXoVSu1gliqPLHo2m98E4hWfZQ="
+        ];
+        trusted-users = [ host.username ];
+        experimental-features = [
+          "nix-command"
+          "flakes"
+        ];
+        # lazy-trees = true; # https://github.com/serokell/deploy-rs/issues/340
+      };
+      channel.enable = false;
+      nixPath = [ "nixpkgs=flake:nixpkgs" ];
+      gc = {
+        automatic = true;
+        dates = "00:00";
+        options = "--delete-older-than 14d";
+      };
+    };
+  };
+}