tadpole: Automatically garbage collect generations

hosts/tadpole/modules/boot/default.nix

@@ -1,10 +1,24 @@
-{ ... }:
+{ inputs, 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 = {
       loader = {
         grub = {
           enable = true;
           device = "/dev/sda";
+
+          configurationLimit = 10;
+        };
       };
     };
   };