fix(vector_stores): refuse MongoDB vector store create with a 400, not a 500

litellm.exception_type passes only litellm's own exception types through
untouched, so the NotImplementedError the search-only refusal raised reached
the caller as APIConnectionError. The proxy served that as a 500 with a
traceback in the body for what is a plain client mistake. Raising
BadRequestError gives the caller a 400 and the message on its own.

litellm/llms/mongodb/vector_stores/transformation.py

@@ -425,7 +425,7 @@ class MongoDBVectorStoreConfig(BaseDirectVectorStoreConfig):
         vector_store_create_optional_params: VectorStoreCreateOptionalRequestParams,
         api_base: str,
     ) -> NoReturn:
-        raise NotImplementedError(_SEARCH_ONLY_MESSAGE)
+        raise config_error(_SEARCH_ONLY_MESSAGE)
 
     def transform_create_vector_store_response(self, response: httpx.Response) -> NoReturn:
-        raise NotImplementedError(_SEARCH_ONLY_MESSAGE)
+        raise config_error(_SEARCH_ONLY_MESSAGE)

tests/test_litellm/llms/mongodb/vector_stores/test_mongodb_transformation.py

@@ -515,15 +515,27 @@ def test_validation_runs_before_any_connection_is_opened():
 
 
 def test_create_vector_store_is_not_supported_and_says_why():
+    """litellm.exception_type only passes its own exception types through untouched, so a
+    NotImplementedError here reaches the caller as APIConnectionError, which the proxy serves
+    as a 500 with a traceback. Refusing an unsupported operation is a client error."""
     config = MongoDBVectorStoreConfig()
 
-    with pytest.raises(NotImplementedError, match="search-only"):
+    with pytest.raises(BadRequestError, match="search-only"):
         config.transform_create_vector_store_request({}, "https://example.test")
 
-    with pytest.raises(NotImplementedError, match="search-only"):
+    with pytest.raises(BadRequestError, match="search-only"):
         config.transform_create_vector_store_response(httpx.Response(200))
 
 
+def test_the_create_refusal_survives_the_public_sdk_error_wrapper():
+    import litellm
+
+    with pytest.raises(BadRequestError) as raised:
+        litellm.vector_stores.create(custom_llm_provider="mongodb", name="anything")
+
+    assert "search-only" in str(raised.value)
+
+
 def test_provider_config_manager_returns_the_mongodb_config():
     config = ProviderConfigManager.get_provider_vector_stores_config(LlmProviders.MONGODB)