From a4467e23ef2fc0852fd427fe568bea4438d1c1dc Mon Sep 17 00:00:00 2001
From: Joseph Doherty <dohejw01@gmail.com>
Date: Thu, 28 May 2026 14:30:39 -0400
Subject: [PATCH] client/python: make LazyBrowseNode.expand concurrency-safe

---
 .../python/src/zb_mom_ww_mxgateway/galaxy.py  | 20 +++++++++------
 clients/python/tests/test_galaxy.py           | 25 ++++++++++++++++++-
 2 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/clients/python/src/zb_mom_ww_mxgateway/galaxy.py b/clients/python/src/zb_mom_ww_mxgateway/galaxy.py
index 42f29e5..8acd4ac 100644
--- a/clients/python/src/zb_mom_ww_mxgateway/galaxy.py
+++ b/clients/python/src/zb_mom_ww_mxgateway/galaxy.py
@@ -292,6 +292,7 @@ class LazyBrowseNode:
         self._options = options
         self._children: list[LazyBrowseNode] = []
         self._is_expanded = False
+        self._expand_lock = asyncio.Lock()
 
     @property
     def object(self) -> galaxy_pb.GalaxyObject:
@@ -317,14 +318,17 @@ class LazyBrowseNode:
         """Fetch direct children of this node; no-op on subsequent calls."""
         if self._is_expanded:
             return
-        new_children: list[LazyBrowseNode] = []
-        async for child in self._client._iter_browse_children(
-            parent_gobject_id=self._object.gobject_id,
-            options=self._options,
-        ):
-            new_children.append(child)
-        self._children.extend(new_children)
-        self._is_expanded = True
+        async with self._expand_lock:
+            if self._is_expanded:
+                return
+            new_children: list[LazyBrowseNode] = []
+            async for child in self._client._iter_browse_children(
+                parent_gobject_id=self._object.gobject_id,
+                options=self._options,
+            ):
+                new_children.append(child)
+            self._children.extend(new_children)
+            self._is_expanded = True
 
 
 async def _canceling_iterator(call: Any) -> AsyncIterator[galaxy_pb.DeployEvent]:
diff --git a/clients/python/tests/test_galaxy.py b/clients/python/tests/test_galaxy.py
index f67ab34..b0bdd0a 100644
--- a/clients/python/tests/test_galaxy.py
+++ b/clients/python/tests/test_galaxy.py
@@ -391,6 +391,28 @@ async def test_browse_expand_idempotent_no_second_rpc() -> None:
     assert len(roots[0].children) == 1
 
 
+@pytest.mark.asyncio
+async def test_browse_expand_concurrent_callers_only_fire_one_rpc() -> None:
+    stub = FakeGalaxyStub()
+    stub.browse_children.replies = [
+        _build_browse_reply([_obj(1, "Plant", is_area=True)], [True], 7),
+        _build_browse_reply([_obj(2, "Mixer_001")], [False], 7),
+    ]
+    client = await GalaxyRepositoryClient.connect(
+        ClientOptions(endpoint="fake", plaintext=True),
+        stub=stub,
+    )
+
+    roots = await client.browse()
+    # Ten concurrent expand calls on the same node should issue exactly one RPC.
+    await asyncio.gather(*(roots[0].expand() for _ in range(10)))
+
+    assert roots[0].is_expanded
+    assert len(roots[0].children) == 1
+    # 1 roots fetch + exactly 1 expand fetch = 2 total
+    assert len(stub.browse_children.requests) == 2
+
+
 @pytest.mark.asyncio
 async def test_browse_expand_unknown_parent_raises_mxgateway_error() -> None:
     stub = FakeGalaxyStub()
@@ -506,7 +528,8 @@ class FakeUnary:
     def __init__(self, replies: list[Any]) -> None:
         self.replies = replies
         self.requests: list[Any] = []
-        self.exceptions: list[BaseException] = []
+        # None entries mean "no exception on this call"; aligns with the replies queue index-by-index.
+        self.exceptions: list[BaseException | None] = []
         self.metadata: tuple[tuple[str, str], ...] | None = None
 
     async def __call__(