pinwheel: Automatically garbage collect generations

hosts/pinwheel/modules/boot/default.nix

@@ -1,5 +1,16 @@
-{ pkgs, ... }:
+{ inputs, pkgs, config, ... }:
 {
+  imports = [ inputs.nix-gc-env.nixosModules.default ];
+
+  config = {
+    nix.gc = {
+      automatic = true;
+      dates = "weekly";
+
+      # `delete_generations` added by nix-gc-env
+      delete_generations = "+${builtins.toString config.boot.loader.systemd-boot.configurationLimit}";
+    };
+
     boot = {
       kernelPackages = pkgs.linuxPackages_latest;
 
@@ -10,7 +21,11 @@
       };
 
       loader = {
-      systemd-boot.enable = true;
+        systemd-boot = {
+          enable = true;
+          configurationLimit = 10;
+        };
+
         efi.canTouchEfiVariables = true;
       };
 
@@ -18,4 +33,5 @@
         "/crypto_keyfile.bin" = null;
       };
     };
+  };
 }