pkgs.writeErofsLayers,profiles/ch-runner: MVE

$ nix-build -A examples.dummy.config.debug.closure.erofs.list | xargs
cat | xargs du -h
749M    /nix/store/bzfv5x6lycq6hzhjv6d6vlk1q8fdg9di-base0.erofs
24M     /nix/store/hp41jfq36y0mmjrzqilyh3jfsvqic3kb-nixos.erofs

$ nix run -f . examples.dummy.config.uvms.cloud-hypervisor.runner
...
<<< Welcome to NixOS 25.11pre-git (x86_64) - ttyS0 >>>

nixos login:

The definition of the `pkgs` fixpoint was moved to pkgs/default.nix.
For that, dirToAttrs was moved to lib/, imported ad hoc

pkgs/writeErofsLayers/package.nix

@@ -0,0 +1,35 @@
+{ lib, writeErofs }:
+{
+  layers,
+  labelLower ? "base",
+  labelUpper ? "image",
+}:
+
+let
+  inherit (lib.lists) toList;
+  nLayers = builtins.length layers;
+  mkLabel = seq: if seq + 1 < nLayers then labelLower + toString seq else labelUpper;
+  f =
+    {
+      roots ? [ ],
+      layers ? [ ],
+      seq ? 0,
+    }:
+    newRoots: {
+      seq = seq + 1;
+      roots = roots ++ (toList newRoots);
+      layers = layers ++ [
+        (writeErofs ({
+          roots = toList newRoots;
+          rootsExclude = roots;
+          passthru = {
+            inherit seq;
+            label = mkLabel seq;
+          };
+          label = mkLabel seq;
+        }))
+      ];
+    };
+  acc = lib.foldl f { } layers;
+in
+acc.layers