Keep Ray integration tests runnable after the Ray 2.55.1 upgrade

Ray 2.55.1 no longer accepts `working_dir=None` in the session fixture, and `uv run pytest` also needs the uv runtime-env hook disabled before importing Ray. This switches the fixture to a temporary working directory and sets the environment variable early enough for the Ray integration tests to keep using the existing pytest entrypoint.

Constraint: Ray 2.55.1 rejects `runtime_env["working_dir"] = None`
Constraint: The project test entrypoint runs through `uv run pytest`
Rejected: Copy the repo into a temporary directory | adds global cwd side effects and more fixture overhead
Rejected: Keep `working_dir=None` and pin older Ray | does not address the upgrade target
Confidence: medium
Scope-risk: narrow
Reversibility: clean
Directive: If the Ray fixture changes again, verify behavior with `uv run pytest`, not only an activated virtualenv
Tested: `uv run pytest tests/integration/test_reads.py -m integration -k 'test_ray_' -vv`
Not-tested: Full integration suite and CI matrix outside the Ray-targeted cases

Author: jx2lee

tests/conftest.py

@@ -3030,13 +3030,19 @@ def pyarrow_table_with_promoted_types(pyarrow_schema_with_promoted_types: "pa.Sc
 
 
 @pytest.fixture(scope="session")
-def ray_session() -> Generator[Any, None, None]:
+def ray_session(tmp_path_factory: pytest.TempPathFactory) -> Generator[Any, None, None]:
     """Fixture to manage Ray initialization and shutdown for tests."""
+    os.environ["RAY_ENABLE_UV_RUN_RUNTIME_ENV"] = (
+        "0"  # Disable Ray's uv-run runtime env propagation to keep test workers isolated.
+    )
+
     import ray
 
+    working_dir = str(tmp_path_factory.mktemp("ray-working-dir"))
+
     ray.init(
         ignore_reinit_error=True,
-        runtime_env={"working_dir": None},  # Prevent Ray from serializing the working directory to workers
+        runtime_env={"working_dir": working_dir},  # Prevent Ray from serializing the working directory to workers
     )
     yield ray
     ray.shutdown()