Add VM self-test configuration for NixOS

modules/hosts/14900k/_private/vm-self.nix

@@ -0,0 +1,44 @@
+# VM self-test overrides — used with nixos-rebuild build-vm to try the system
+# in a VM without rebuilding/rebooting the host.
+{ config, lib, pkgs, ... }:
+{
+  virtualisation.vmVariant = {
+    config = {
+
+
+      hardware.nvidia-container-toolkit.enable = lib.mkForce false;
+      hardware.nvidia.package = lib.mkForce null;
+      services.xserver.videoDrivers = lib.mkForce [ "modesetting" ];
+
+      virtualisation = {
+        memorySize = 4096;
+        cores = 3;
+        graphics = true;
+        qemu.options = [
+          "-device virtio-vga-gl"
+          "-display gtk,gl=on"
+        ];
+      };
+
+      users.users.olivier = {
+        initialPassword = lib.mkForce "";
+        hashedPasswordFile = lib.mkForce null; # Disable the secret file dependency
+      };
+
+      # Force greetd's `initial_session` directly. We can't rely on
+      # `services.displayManager.autoLogin` because DankGreeter's flake module
+      # (inputs.dms.nixosModules.greeter) aggressively overwrites
+      # `services.greetd.settings`, clobbering whatever the displayManager
+      # module injects for auto-login. mkForce on `initial_session` alone wins
+      # against DMS without touching `default_session` (DankGreeter), so a
+      # manual logout in the VM still shows DankGreeter. VM-only — host build
+      # is unaffected because this whole block lives under vmVariant.
+      services.greetd.settings.initial_session = lib.mkForce {
+        command = "${pkgs.niri}/bin/niri-session";
+        user = "olivier";
+      };
+
+      environment.systemPackages = [ pkgs.grc ];
+    };
+  };
+}

modules/hosts/14900k/configuration.nix

@@ -15,6 +15,7 @@
         self.nixosModules."client-services"
         ./_private/platform.nix
         ./_private/nvidia.nix
+        ./_private/vm-self.nix
         ./_private/gpu-passthru.nix
         ./_private/peripherals.nix
         # ./_private/printing-epson.nix