Add impermanence implementation.

nodes/hosts/lappy/configuration.nix

@@ -2,12 +2,13 @@
 # your system. Help is available in the configuration.nix(5) man page, on
 # https://search.nixos.org/options and in the NixOS manual (`nixos-help`).
 
-{ config, lib, pkgs, ... }:
+{ config, lib, pkgs, inputs, ... }:
 
 {
   imports =
     [ # Include the results of the hardware scan.
       ./hardware-configuration.nix
+      ./impermanence.nix
       ./programs/sof-firmware.nix
       # Not working yet.
       #./services/fprintd.nix

nodes/hosts/lappy/impermanence.nix

@@ -0,0 +1,41 @@
+{lib, ...}: {
+  #  Reset root subvolume on boot
+  boot.initrd.postResumeCommands = lib.mkAfter ''
+    mkdir /btrfs_tmp
+      mount /dev/mapper/cryptroot /btrfs_tmp # CONFIRM THIS IS CORRECT FROM findmnt
+      if [[ -e /btrfs_tmp/root ]]; then
+        mkdir -p /btrfs_tmp/old_roots
+        timestamp=$(date --date="@$(stat -c %Y /btrfs_tmp/root)" "+%Y-%m-%-d_%H:%M:%S")
+        mv /btrfs_tmp/root "/btrfs_tmp/old_roots/$timestamp"
+      fi
+
+      delete_subvolume_recursively() {
+        IFS=$'\n'
+        for i in $(btrfs subvolume list -o "$1" | cut -f 9- -d ' '); do
+          delete_subvolume_recursively "/btrfs_tmp/$i"
+        done
+        btrfs subvolume delete "$1"
+      }
+
+      for i in $(find /btrfs_tmp/old_roots/ -maxdepth 1 -mtime +30); do
+        delete_subvolume_recursively "$i"
+      done
+
+      btrfs subvolume create /btrfs_tmp/root
+      umount /btrfs_tmp
+  '';
+
+  # Use /persist as the persistence root, matching Disko's mountpoint
+  environment.persistence."/nix/persist" = {
+    hideMounts = true;
+    directories = [
+      "/etc" # System configuration (Keep this here for persistence via bind-mount)
+      "/var/spool" # Mail queues, cron jobs
+      "/srv" # Web server data, etc.
+      "/root"
+      "/home"
+    ];
+    files = [
+    ];
+  };
+}