failed nixbsd experiment

modules/system/nix.nix

@@ -6,14 +6,48 @@ let
     else if config.boot.loader.systemd-boot.enable then 
       config.boot.loader.systemd-boot.configurationLimit
     else null;
+
+  # NixBSD builder VM SSH key (needs to be readable by root/nix-daemon)
+  builderKeyDir = "/etc/nix/builder-keys";
 in 
 {
   nix = {
     daemonIOSchedClass = "idle";
     daemonCPUSchedPolicy = "idle";
     settings.trusted-users = [ "root" "user" ];
+
+    # FreeBSD remote builder VM (NixBSD)
+    distributedBuilds = true;
+    buildMachines = [
+      {
+        hostName = "192.168.122.100";
+        system = "x86_64-freebsd";
+        sshUser = "root";
+        sshKey = "${builderKeyDir}/nixbsd-builder";
+        maxJobs = 8;
+        speedFactor = 1;
+        supportedFeatures = [ "big-parallel" ];
+      }
+    ];
+    settings.builders-use-substitutes = true;
   };
 
+  # Install the builder SSH key where root/nix-daemon can read it
+  system.activationScripts.nixbsd-builder-key = ''
+    mkdir -p ${builderKeyDir}
+    cp /home/user/Projects/nixbsd-flake/keys/builder ${builderKeyDir}/nixbsd-builder
+    chmod 600 ${builderKeyDir}/nixbsd-builder
+    chown root:root ${builderKeyDir}/nixbsd-builder
+  '';
+
+  # Skip host key checking for the local builder VM (keys change on rebuild)
+  programs.ssh.extraConfig = ''
+    Host 192.168.122.100
+      StrictHostKeyChecking no
+      UserKnownHostsFile /dev/null
+      LogLevel ERROR
+  '';
+
   # Clean up nix store from old configurations usinx nix-sweep
   services.nix-sweep = {
     enable = true;