feat(api-core): centralize endpoint routing and universe domain resolution

packages/google-api-core/google/api_core/gapic_v1/__init__.py

@@ -25,10 +25,12 @@
 # Older Python versions safely ignore this variable.
 __lazy_modules__: Set[str] = {
     "google.api_core.gapic_v1.client_info",
+    "google.api_core.gapic_v1.client_utils",
     "google.api_core.gapic_v1.requests",
     "google.api_core.gapic_v1.routing_header",
 }
-__all__ = ["client_info", "requests", "routing_header"]
+__all__ = ["client_info", "client_utils", "requests", "routing_header"]
+
 
 if _has_grpc:
     __lazy_modules__.update(
@@ -42,6 +44,7 @@
 
 from google.api_core.gapic_v1 import (  # noqa: E402
     client_info,
+    client_utils,
     requests,
     routing_header,
 )

packages/google-api-core/google/api_core/gapic_v1/client_utils.py

@@ -0,0 +1,24 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+"""Helpers for client setup and configuration."""
+
+from google.api_core.universe import (
+    get_universe_domain,
+)
+
+__all__ = [
+    "get_universe_domain",
+]

packages/google-api-core/tests/conftest.py

@@ -0,0 +1,31 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os
+from unittest import mock
+
+import pytest
+
+
+@pytest.fixture(scope="session", autouse=True)
+def mock_mtls_env():
+    """Autouse session-scoped fixture to isolate unit tests from workstation mTLS environments."""
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield

packages/google-api-core/tests/unit/gapic/test_client_utils.py

@@ -0,0 +1,20 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from google.api_core.gapic_v1 import client_utils
+from google.api_core import universe
+
+
+def test_exports():
+    assert client_utils.get_universe_domain is universe.get_universe_domain