diff --git a/test/fixtures/test-parallel.behavior.json b/test/fixtures/test-parallel.behavior.json
index 8982c7595e9..c0fa529ca42 100644
--- a/test/fixtures/test-parallel.behavior.json
+++ b/test/fixtures/test-parallel.behavior.json
@@ -185,6 +185,14 @@
       {
         "file": "extensions/tavily/src/tavily-search-tool.test.ts",
         "reason": "This search-tool suite hoists the Tavily client mock and imports lazily; keep it isolated so shared extension workers do not bypass the mocked client via cached modules."
+      },
+      {
+        "file": "extensions/xai/provider.contract.test.ts",
+        "reason": "This xAI provider contract suite validates the bundled provider registration produced by defineSingleProviderPluginEntry; keep it in its own forked extension lane so shared workers cannot poison that registry with hoisted plugin-sdk mocks from unrelated extension files."
+      },
+      {
+        "file": "extensions/xai/web-search-provider.contract.test.ts",
+        "reason": "This xAI web-search contract suite validates the bundled Grok web-search registration from the same xAI plugin entry; keep it isolated so shared extension workers do not reuse hoisted plugin-sdk web-search mocks from unrelated extension files."
       }
     ]
   },