Another test case.

tests/networkd-phobos.nix

@@ -0,0 +1,41 @@
+# tests/networkd-phobos.nix
+let
+  system = "x86_64-linux";
+
+  pkgs = import <nixpkgs> { inherit system; };
+  lib = pkgs.lib;
+
+  meta = import ../meta.nix;
+  addressing = import ../lib/addressing { inherit lib; };
+
+  nixos = lib.nixosSystem {
+    inherit system;
+
+    modules = [
+      # Your core Metanix module (the one you moved)
+      ../modules/metanix/core.nix
+
+      # The systemd-networkd integration you pasted
+      ../modules/metanix/networkd.nix
+
+      # Inline module to wire meta/addressing + identify this host
+      {
+        # Metanix world & library
+        inherit meta addressing;
+
+        # Who am I?
+        networking.hostName = "phobos";
+        # Optional override; here it matches hostName anyway
+        metanix.thisHost = "phobos";
+
+        # You can also stub other things here if needed
+      }
+    ];
+  };
+in
+{
+  # What we care about inspecting:
+  systemdNetwork = nixos.config.systemd.network;
+  metanixHost = nixos.config.metanix.network.hosts.phobos;
+  metanixSubnet = nixos.config.metanix.network.subnets."home-main";
+}