From 1fddf90b75467be46bba5e2c1e95d1b54b450c4e Mon Sep 17 00:00:00 2001
From: Anmol Jaiswal <anmolg1997@users.noreply.github.com>
Date: Tue, 10 Feb 2026 19:37:56 +0530
Subject: [PATCH 1/2] fix(sessions): use async iteration for
 VertexAiSessionService.list_sessions pagination

The sessions_iterator returned by api_client.agent_engines.sessions.list()
is an AsyncPager that only fetches additional pages when consumed via
async iteration (__aiter__/__anext__). Using a synchronous `for` loop
only retrieved the first page (~100 sessions), silently dropping all
subsequent pages.

Changed `for` to `async for` to enable proper async pagination,
allowing all sessions to be returned regardless of count.

Fixes #4302
---
 .../adk/sessions/vertex_ai_session_service.py |  2 +-
 .../test_vertex_ai_session_service.py         | 23 ++++++++++++++-----
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/src/google/adk/sessions/vertex_ai_session_service.py b/src/google/adk/sessions/vertex_ai_session_service.py
index f5cafee467..1837a907eb 100644
--- a/src/google/adk/sessions/vertex_ai_session_service.py
+++ b/src/google/adk/sessions/vertex_ai_session_service.py
@@ -215,7 +215,7 @@ async def list_sessions(
           config=config,
       )
 
-      for api_session in sessions_iterator:
+      async for api_session in sessions_iterator:
         sessions.append(
             Session(
                 app_name=app_name,
diff --git a/tests/unittests/sessions/test_vertex_ai_session_service.py b/tests/unittests/sessions/test_vertex_ai_session_service.py
index 12a11a93a2..fdc903c3df 100644
--- a/tests/unittests/sessions/test_vertex_ai_session_service.py
+++ b/tests/unittests/sessions/test_vertex_ai_session_service.py
@@ -264,6 +264,17 @@ async def to_async_iterator(data):
     yield item
 
 
+class AsyncIterableList(list):
+  """A list that also supports async iteration, mimicking AsyncPager behavior."""
+
+  def __aiter__(self):
+    return self._async_iter()
+
+  async def _async_iter(self):
+    for item in self:
+      yield item
+
+
 class MockAsyncClient:
   """Mocks the API Client."""
 
@@ -300,20 +311,20 @@ async def _list_sessions(self, name: str, config: dict[str, Any]):
     if user_id_match:
       user_id = user_id_match.group(1)
       if user_id == 'user_with_pages':
-        return [
+        return AsyncIterableList([
             _convert_to_object(MOCK_SESSION_JSON_PAGE1),
             _convert_to_object(MOCK_SESSION_JSON_PAGE2),
-        ]
-      return [
+        ])
+      return AsyncIterableList([
           _convert_to_object(session)
           for session in self.session_dict.values()
           if session['user_id'] == user_id
-      ]
+      ])
 
     # No user filter, return all sessions
-    return [
+    return AsyncIterableList([
         _convert_to_object(session) for session in self.session_dict.values()
-    ]
+    ])
 
   async def _delete_session(self, name: str):
     session_id = name.split('/')[-1]

From 14c71b607ecbf2215f4b9ba6eb4b0ff6b9eaf740 Mon Sep 17 00:00:00 2001
From: Liang Wu <18244712+wuliang229@users.noreply.github.com>
Date: Tue, 10 Feb 2026 16:16:27 -0800
Subject: [PATCH 2/2] Apply suggestions from code review

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
---
 tests/unittests/sessions/test_vertex_ai_session_service.py | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/tests/unittests/sessions/test_vertex_ai_session_service.py b/tests/unittests/sessions/test_vertex_ai_session_service.py
index fdc903c3df..dc6ef08b4a 100644
--- a/tests/unittests/sessions/test_vertex_ai_session_service.py
+++ b/tests/unittests/sessions/test_vertex_ai_session_service.py
@@ -267,10 +267,7 @@ async def to_async_iterator(data):
 class AsyncIterableList(list):
   """A list that also supports async iteration, mimicking AsyncPager behavior."""
 
-  def __aiter__(self):
-    return self._async_iter()
-
-  async def _async_iter(self):
+  async def __aiter__(self):
     for item in self:
       yield item