fix(tools): run AgentTool nested agent in unary mode

`AgentTool.run_async` does not forward the nested run's events to the caller; it
only uses the last event's content as the tool response. That content is complete
in unary mode and in aggregated streaming, but a caller streaming without
aggregation would leave only a partial chunk in the last event. Since the nested
events are never surfaced anyway, always run the wrapped agent under
`StreamingMode.NONE` (via a per-call RunConfig copy that leaves the caller's
config untouched).

PiperOrigin-RevId: 970844321

Author: google-genai-bot

src/google/adk/tools/agent_tool.py

@@ -26,6 +26,7 @@
 from typing_extensions import override
 
 from . import _automatic_function_calling_util
+from ..agents._streaming_mode import StreamingMode
 from ..agents.common_configs import AgentRefConfig
 from ..events._branch_path import _BranchPath
 from ..features import FeatureName
@@ -301,6 +302,17 @@ async def run_async(
       nested_run_config = nested_run_config.model_copy(
           update={'support_cfc': False}
       )
+    if (
+        nested_run_config is not None
+        and nested_run_config.streaming_mode != StreamingMode.NONE
+    ):
+      # The nested run's events are not forwarded to the caller; only the last
+      # event's content becomes the response. That is complete in unary mode and
+      # in aggregated streaming, but a caller streaming without aggregation
+      # would leave only a partial chunk in the last event, so always run unary.
+      nested_run_config = nested_run_config.model_copy(
+          update={'streaming_mode': StreamingMode.NONE}
+      )
 
     last_content = None
     last_error_message = None

tests/unittests/tools/test_agent_tool.py

@@ -24,6 +24,7 @@
 from google.adk.agents.llm_agent import Agent
 from google.adk.agents.llm_agent import LlmAgent
 from google.adk.agents.run_config import RunConfig
+from google.adk.agents.run_config import StreamingMode
 from google.adk.agents.sequential_agent import SequentialAgent
 from google.adk.artifacts.in_memory_artifact_service import InMemoryArtifactService
 from google.adk.events.event import Event
@@ -291,6 +292,35 @@ async def test_agent_tool_does_not_forward_support_cfc(monkeypatch):
   assert parent_run_config.support_cfc is True
 
 
+@mark.asyncio
+async def test_agent_tool_forces_unary_nested_run(monkeypatch):
+  """The response is read from the last event, so the nested run must be unary."""
+  parent_run_config = RunConfig(
+      streaming_mode=StreamingMode.SSE, max_llm_calls=7
+  )
+
+  nested_run_config = await _capture_nested_run_config(
+      monkeypatch, parent_run_config
+  )
+
+  assert nested_run_config.streaming_mode == StreamingMode.NONE
+  # Other settings are still forwarded, and the caller is left untouched.
+  assert nested_run_config.max_llm_calls == 7
+  assert parent_run_config.streaming_mode == StreamingMode.SSE
+
+
+@mark.asyncio
+async def test_agent_tool_keeps_unary_run_unchanged(monkeypatch):
+  """A caller already running unary is forwarded unchanged."""
+  parent_run_config = RunConfig(streaming_mode=StreamingMode.NONE)
+
+  nested_run_config = await _capture_nested_run_config(
+      monkeypatch, parent_run_config
+  )
+
+  assert nested_run_config.streaming_mode == StreamingMode.NONE
+
+
 def test_no_schema():
   mock_model = testing_utils.MockModel.create(
       responses=[