Update configuration.nix

configuration.nix

@@ -200,7 +200,7 @@
   };
 
   systemd.timers.nixos-git-update = {
-    description = "Check for config updates hourly";
+    description = "Check for config updates at startup";
     wantedBy = [ "timers.target" ];
     timerConfig = {
       OnBootSec = "60s";
@@ -213,6 +213,32 @@
 
   zramSwap.enable = true;
 
+  ############################################################
+  # USB ROOT DEVICE MONITOR (SHUTDOWN ON DISCONNECT)
+  ############################################################
+
+  systemd.services.usb-root-monitor = {
+    description = "Monitor USB root device and shut down if removed";
+    script = ''
+      while true; do
+        if ! test -e /dev/disk/by-label/nixos-root; then
+          /run/current-system/sw/bin/logger -t usb-root-monitor "Root device missing – shutting down"
+          /run/current-system/sw/bin/systemctl poweroff
+          exit 0
+        fi
+        sleep 5
+      done
+    '';
+    serviceConfig = {
+      Type = "simple";
+      Restart = "always";
+      RestartSec = 10;
+      User = "root";
+      ExecStop = "/run/current-system/sw/bin/kill $MAINPID";
+    };
+    wantedBy = [ "multi-user.target" ];
+  };
+
   ############################################################
   # NIXOS VERSION
   ############################################################