Serialize NordVPN bootstrap and reconciliation

tests/unit/StoreAndInspectorTest.php

@@ -3,6 +3,7 @@
 use OPNsense\NordVPN\EndpointStore;
 use OPNsense\NordVPN\EnrollmentInspector;
 use OPNsense\NordVPN\NordApi;
+use OPNsense\NordVPN\ReconciliationLock;
 use OPNsense\NordVPN\StatusStore;
 use PHPUnit\Framework\TestCase;
 
@@ -58,4 +59,25 @@ final class StoreAndInspectorTest extends TestCase
 
         unlink($path);
     }
+
+    public function testReconciliationLockRejectsConcurrentOperations(): void
+    {
+        $path = sys_get_temp_dir() . '/nordvpn-lock-' . bin2hex(random_bytes(8));
+        $first = new ReconciliationLock($path);
+        $second = new ReconciliationLock($path);
+
+        $first->acquire();
+        try {
+            $second->acquire();
+            $this->fail('A concurrent operation acquired the lock.');
+        } catch (RuntimeException $exception) {
+            $this->assertSame('A NordVPN operation is already running.', $exception->getMessage());
+        } finally {
+            $first->release();
+        }
+
+        $second->acquire();
+        $second->release();
+        unlink($path);
+    }
 }