Two years later, actually functional output.

tests/networkd-phobos.nix

@@ -2,40 +2,49 @@
 let
   system = "x86_64-linux";
 
+  # Bring in nixpkgs and lib
   pkgs = import <nixpkgs> { inherit system; };
   lib = pkgs.lib;
 
+  # Your world + addressing lib
   meta = import ../meta.nix;
   addressing = import ../lib/addressing { inherit lib; };
 
-  nixos = lib.nixosSystem {
-    inherit system;
+  # NixOS module system library
+  nixosLib = import <nixpkgs/nixos/lib> {
+    inherit lib;
+  };
 
-    modules = [
-      # Your core Metanix module (the one you moved)
+  # All standard NixOS modules (as a list)
+  baseModules = import <nixpkgs/nixos/modules/module-list.nix>;
+
+  # Evaluate modules as if this were a NixOS system
+  evalResult = nixosLib.evalModules {
+    modules =
+      baseModules
+      ++ [
+        # Metanix core wiring (meta + addressing)
         ../modules/metanix/core.nix
 
-      # The systemd-networkd integration you pasted
+        # systemd-networkd integration
         ../modules/metanix/networkd.nix
 
-      # Inline module to wire meta/addressing + identify this host
+        # Local stub: "this machine is phobos"
         {
-        # 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
         }
       ];
+
+    # Args passed to all modules: { lib, pkgs, system, meta, addressing, modulesPath, ... }
+    specialArgs = {
+      inherit lib pkgs system meta addressing;
+      modulesPath = builtins.toString <nixpkgs/nixos/modules>;
+    };
   };
 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";
+  systemdNetwork = evalResult.config.systemd.network;
+  metanixHost = evalResult.config.metanix.network.hosts.phobos;
+  metanixSubnet = evalResult.config.metanix.network.subnets."home-main";
 }