use erofs w/zstd compression. clean up a bit.

modules/kernel.nix

@@ -0,0 +1,13 @@
+{ pkgs, ... }:
+{
+  boot.kernelPackages = pkgs.linuxPackages_6_11;
+  boot.kernelPatches = [
+    {
+      # name = "crashdump-config";
+      patch = null;
+      extraConfig = ''
+        EROFS_FS_ZIP_ZSTD y
+      '';
+    }
+  ];
+}

modules/partitions.nix

@@ -19,6 +19,14 @@
       name = config.boot.uki.name;
       split = true;
 
+      mkfsOptions = {
+        erofs = [
+          "-zzstd,5" # Zstd compression
+          "-T0" # Fixed timestamp for all files
+          "-Efragments,dedupe,ztailpacking" # Extended options
+        ];
+      };
+
       partitions = {
         "esp" = {
           contents = {
@@ -48,8 +56,8 @@
           repartConfig = {
             Type = "linux-generic";
             Label = "${config.boot.uki.name}_${config.system.image.version}";
-            Format = "squashfs";
-            Minimize = "off";
+            Format = "erofs";
+            Minimize = "best";
             ReadOnly = "yes";
 
             SizeMinBytes = "1G";