Add GC

modules/common.nix

@@ -7,5 +7,6 @@
     ./common/services.nix
     ./common/networking.nix
     ./common/system.nix
+    ./common/garbage-collection.nix
   ];
 }

modules/common/garbage-collection.nix

@@ -0,0 +1,31 @@
+{ config, lib, pkgs, ... }:
+
+{
+  # ─────────────────────────────────────────────
+  # Bootloader generation limit (rollback window)
+  # ─────────────────────────────────────────────
+  boot.loader.systemd-boot.configurationLimit = 3;
+  # If you're using GRUB instead, use this instead:
+  # boot.loader.grub.configurationLimit = 3;
+
+  # ─────────────────────────────────────────────
+  # Nix garbage collection (tight retention)
+  # ─────────────────────────────────────────────
+  nix.gc = {
+    automatic = true;
+    dates = "daily";
+    options = "--delete-older-than 3d";
+  };
+
+  # ─────────────────────────────────────────────
+  # Store optimisation (reduce disk bloat)
+  # ─────────────────────────────────────────────
+  nix.settings.auto-optimise-store = true;
+
+  # ─────────────────────────────────────────────
+  # Optional: keep system leaner overall
+  # (reduces leftover system profiles slightly)
+  # ─────────────────────────────────────────────
+  nix.settings.keep-outputs = false;
+  nix.settings.keep-derivations = false;
+}