Put impermanence behind an option to make kopia work.

common/container-node.nix

@@ -1,9 +1,11 @@
 { lib, ... }:
 {
   imports = [
+    ./impermanence.nix  # TODO: find a way to avoid needing this here
   ];
 
   boot.isContainer = true;
+  custom.impermanence.enable = false;
   custom.tailscale.enable = false;
   networking.useDHCP = lib.mkForce false;
 }

common/impermanence.nix

@@ -1,5 +1,17 @@
-{ pkgs, inputs, ... }:
+{ pkgs, inputs, lib, config, ... }:
+let
+  cfg = config.custom.impermanence;
+in
 {
+  options.custom.impermanence = {
+    enable = lib.mkOption {
+      type = lib.types.bool;
+      default = true;
+      description = "Enable impermanent root fs";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
     environment.persistence = {
       "/persist" = {
         directories = [ "/var/lib/nixos" ];
@@ -68,4 +80,5 @@
       btrfs subvolume create /mnt/root
       umount /mnt
     '';
+  };
 }