Add back the PineBook for later and make etc immutable

hosts/axolotl/boot/default.nix

@@ -0,0 +1,40 @@
+{ pkgs, ... }:
+{
+  boot = {
+    kernelPackages = pkgs.linuxPackages_latest;
+    kernel.sysctl."vm.max_map_count" = 2147483642;
+
+    initrd = {
+      systemd = {
+        enable = true;
+        services.root-reset = {
+          description = "Reset BTRFS root and snapshot last boot";
+          wantedBy = [ "initrd.target" ];
+          after = [ "dev-nixos-root.device" ];
+          before = [ "sysroot.mount" ];
+          unitConfig.DefaultDependencies = "no";
+          serviceConfig.Type = "oneshot";
+          script = ''
+            mkdir -p /mnt
+            mount /dev/nixos/root /mnt
+
+            if [[ -e /mnt/@prev ]]; then
+              btrfs subvolume delete /mnt/@prev
+            fi
+
+            btrfs subvolume snapshot /mnt/@ /mnt/@prev
+
+            btrfs subvolume list -o /mnt/@ | cut -f9 -d' ' | while read subvolume; do
+              btrfs subvolume delete "/mnt/$subvolume"
+            done
+
+            btrfs subvolume delete /mnt/@
+            btrfs subvolume create /mnt/@
+
+            umount /mnt
+          '';
+	};
+      };
+    };
+  };
+}