fix: allows current sub-agent to finish execution before exiting the loop agent due to a sub-agent's escalation. This commit also disables the summarization for exit_loop tool

Fixes #423

Related to #1670

- This avoids the `GeneratorExit` error thrown, which would crash OTel metric collection and cause `Failed to detach context` error.
- This also allows all function  calls are processed when exit_loop is called together with other tools in the same LLmResponse.

A sample agent for testing:

```
from google.adk import Agent
from google.adk.agents.loop_agent import LoopAgent
from google.adk.tools.exit_loop_tool import exit_loop

worker_1 = Agent(
    name='worker_1',
    description='Worker 1',
    instruction="""\
Just say job #1 is done.

If job #1 is said to be done. Call exit_loop tool.""",
    tools=[exit_loop],
)

worker_2 = Agent(
    name='worker_2',
    description='Worker 2',
    instruction="""\
Just say job #2 is done.

If job #2 is said to be done. Call exit_loop tool.""",
    tools=[exit_loop],
)

work_agent = LoopAgent(
    name='work_agent',
    description='Do all work.',
    sub_agents=[worker_1, worker_2],
    max_iterations=5,
)

root_agent = Agent(
    model='gemini-2.0-flash',
    name='hello_world_agent',
    description='hello world agent that can roll a  check prime',
    instruction="""Hand off works to sub agents.""",
    sub_agents=[work_agent],
)
```
PiperOrigin-RevId: 785538101

src/google/adk/agents/loop_agent.py

@@ -53,10 +53,15 @@ class LoopAgent(BaseAgent):
     times_looped = 0
     while not self.max_iterations or times_looped < self.max_iterations:
       for sub_agent in self.sub_agents:
+        should_exit = False
         async for event in sub_agent.run_async(ctx):
           yield event
           if event.actions.escalate:
-            return
+            should_exit = True
+
+        if should_exit:
+          return
+
       times_looped += 1
     return
 

src/google/adk/tools/exit_loop_tool.py

@@ -21,3 +21,4 @@ def exit_loop(tool_context: ToolContext):
   Call this function only when you are instructed to do so.
   """
   tool_context.actions.escalate = True
+  tool_context.actions.skip_summarization = True

tests/unittests/agents/test_loop_agent.py

@@ -68,6 +68,13 @@ class _TestingAgentWithEscalateAction(BaseAgent):
         ),
         actions=EventActions(escalate=True),
     )
+    yield Event(
+        author=self.name,
+        invocation_id=ctx.invocation_id,
+        content=types.Content(
+            parts=[types.Part(text=f'I have done my job after escalation!!')]
+        ),
+    )
 
 
 async def _create_parent_invocation_context(
@@ -115,9 +122,12 @@ async def test_run_async_with_escalate_action(request: pytest.FixtureRequest):
   escalating_agent = _TestingAgentWithEscalateAction(
       name=f'{request.function.__name__}_test_escalating_agent'
   )
+  ignored_agent = _TestingAgent(
+      name=f'{request.function.__name__}_test_ignored_agent'
+  )
   loop_agent = LoopAgent(
       name=f'{request.function.__name__}_test_loop_agent',
-      sub_agents=[non_escalating_agent, escalating_agent],
+      sub_agents=[non_escalating_agent, escalating_agent, ignored_agent],
   )
   parent_ctx = await _create_parent_invocation_context(
       request.function.__name__, loop_agent
@@ -125,7 +135,7 @@ async def test_run_async_with_escalate_action(request: pytest.FixtureRequest):
   events = [e async for e in loop_agent.run_async(parent_ctx)]
 
   # Only two events are generated because the sub escalating_agent escalates.
-  assert len(events) == 2
+  assert len(events) == 3
   assert events[0].author == non_escalating_agent.name
   assert events[1].author == escalating_agent.name
   assert events[0].content.parts[0].text == (
@@ -134,3 +144,6 @@ async def test_run_async_with_escalate_action(request: pytest.FixtureRequest):
   assert events[1].content.parts[0].text == (
       f'Hello, async {escalating_agent.name}!'
   )
+  assert (
+      events[2].content.parts[0].text == 'I have done my job after escalation!!'
+  )

tests/unittests/flows/llm_flows/test_agent_transfer.py

@@ -303,11 +303,9 @@ def test_auto_to_loop():
               name='exit_loop', response={'result': None}
           ),
       ),
-      # root_agent summarizes.
-      ('root_agent', 'response4'),
   ]
 
   # root_agent should still be the current agent because sub_agent_1 is loop.
   assert testing_utils.simplify_events(runner.run('test2')) == [
-      ('root_agent', 'response5'),
+      ('root_agent', 'response4'),
   ]