Resolve Client.Python-003, -005, -009 code-review findings

Client.Python-003: stream_events_raw and query_active_alarms passed `timeout`
to the stub with no TypeError fallback, unlike _unary. Both now route through
a shared _open_stream helper that strips `timeout` on TypeError.

Client.Python-005: discover_hierarchy buffered the entire Galaxy hierarchy in
memory. Added GalaxyRepositoryClient.iter_hierarchy, a lazy async generator
yielding objects page-by-page; discover_hierarchy is now a thin wrapper that
preserves its list contract. README documents iter_hierarchy.

Client.Python-009: added regression coverage for previously untested paths —
write2/add_item2 request shape, the MAX_BULK_ITEMS boundary, the None-argument
TypeError guards, TLS ca_file reading, and the non-auth map_rpc_error fallthrough.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/python/tests/test_galaxy_iter_hierarchy.py

@@ -0,0 +1,127 @@
+"""Regression tests for Client.Python-005: streaming hierarchy iteration.
+
+`GalaxyRepositoryClient.iter_hierarchy` yields objects page by page instead of
+buffering the entire Galaxy hierarchy in memory, and `discover_hierarchy`
+remains a convenience wrapper built on top of it.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+import pytest
+
+from mxgateway import ClientOptions, GalaxyRepositoryClient
+from mxgateway.generated import galaxy_repository_pb2 as galaxy_pb
+
+
+class _FakeUnary:
+    def __init__(self, replies: list[Any]) -> None:
+        self.replies = list(replies)
+        self.requests: list[Any] = []
+        self.metadata: tuple[tuple[str, str], ...] | None = None
+
+    async def __call__(
+        self,
+        request: Any,
+        *,
+        metadata: tuple[tuple[str, str], ...],
+        timeout: float | None = None,
+    ) -> Any:
+        self.requests.append(request)
+        self.metadata = metadata
+        return self.replies.pop(0)
+
+
+class _FakeGalaxyStub:
+    def __init__(self, discover_replies: list[Any]) -> None:
+        self.DiscoverHierarchy = _FakeUnary(discover_replies)
+
+
+def _two_page_replies() -> list[galaxy_pb.DiscoverHierarchyReply]:
+    return [
+        galaxy_pb.DiscoverHierarchyReply(
+            next_page_token="page-2",
+            total_object_count=3,
+            objects=[
+                galaxy_pb.GalaxyObject(gobject_id=1, tag_name="Area_001", is_area=True),
+                galaxy_pb.GalaxyObject(gobject_id=2, tag_name="Pump_001"),
+            ],
+        ),
+        galaxy_pb.DiscoverHierarchyReply(
+            total_object_count=3,
+            objects=[
+                galaxy_pb.GalaxyObject(gobject_id=3, tag_name="Pump_002"),
+            ],
+        ),
+    ]
+
+
+@pytest.mark.asyncio
+async def test_iter_hierarchy_yields_objects_across_pages() -> None:
+    stub = _FakeGalaxyStub(_two_page_replies())
+    client = await GalaxyRepositoryClient.connect(
+        ClientOptions(endpoint="fake", plaintext=True),
+        stub=stub,
+    )
+
+    tags = [obj.tag_name async for obj in client.iter_hierarchy()]
+
+    assert tags == ["Area_001", "Pump_001", "Pump_002"]
+    assert len(stub.DiscoverHierarchy.requests) == 2
+    assert stub.DiscoverHierarchy.requests[0].page_token == ""
+    assert stub.DiscoverHierarchy.requests[1].page_token == "page-2"
+
+
+@pytest.mark.asyncio
+async def test_iter_hierarchy_is_lazy_and_does_not_prefetch_next_page() -> None:
+    """Pulling only the first object must not have requested the second page."""
+
+    stub = _FakeGalaxyStub(_two_page_replies())
+    client = await GalaxyRepositoryClient.connect(
+        ClientOptions(endpoint="fake", plaintext=True),
+        stub=stub,
+    )
+
+    iterator = client.iter_hierarchy()
+    first = await iterator.__anext__()
+
+    assert first.tag_name == "Area_001"
+    # Only the first page should have been fetched so far.
+    assert len(stub.DiscoverHierarchy.requests) == 1
+
+    await iterator.aclose()
+
+
+@pytest.mark.asyncio
+async def test_iter_hierarchy_rejects_repeated_page_token() -> None:
+    stub = _FakeGalaxyStub(
+        [
+            galaxy_pb.DiscoverHierarchyReply(next_page_token="7:1"),
+            galaxy_pb.DiscoverHierarchyReply(next_page_token="7:1"),
+        ],
+    )
+    client = await GalaxyRepositoryClient.connect(
+        ClientOptions(endpoint="fake", plaintext=True),
+        stub=stub,
+    )
+
+    with pytest.raises(Exception, match="repeated page token"):
+        async for _ in client.iter_hierarchy():
+            pass
+
+
+@pytest.mark.asyncio
+async def test_discover_hierarchy_still_returns_full_list() -> None:
+    """The convenience wrapper must keep returning a buffered list."""
+
+    stub = _FakeGalaxyStub(_two_page_replies())
+    client = await GalaxyRepositoryClient.connect(
+        ClientOptions(endpoint="fake", plaintext=True),
+        stub=stub,
+    )
+
+    objects = await client.discover_hierarchy()
+
+    assert isinstance(objects, list)
+    assert [obj.tag_name for obj in objects] == ["Area_001", "Pump_001", "Pump_002"]