feat(tools): Add an option to disallow propagating runner plugins to AgentTool runner

Merge https://github.com/google/adk-python/pull/2779

Fixes #2780

### testing plan
not available as is doesn't introduce new functionality

Co-authored-by: Wei Sun (Jack) <weisun@google.com>
COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/2779 from davidkl97:feature/agent-tool-plugins a602c808789f3daeed6244e352a6fb8fb6972de3
PiperOrigin-RevId: 835366974

tests/unittests/tools/test_agent_tool.py

@@ -570,3 +570,112 @@ def test_agent_tool_response_schema_with_input_schema_no_output_vertex_ai(
   # Should have string response schema for VERTEX_AI when no output_schema
   assert declaration.response is not None
   assert declaration.response.type == types.Type.STRING
+
+
+def test_include_plugins_default_true():
+  """Test that plugins are propagated by default (include_plugins=True)."""
+
+  # Create a test plugin that tracks callbacks
+  class TrackingPlugin(BasePlugin):
+
+    def __init__(self, name: str):
+      super().__init__(name)
+      self.before_agent_calls = 0
+
+    async def before_agent_callback(self, **kwargs):
+      self.before_agent_calls += 1
+
+  tracking_plugin = TrackingPlugin(name='tracking')
+
+  mock_model = testing_utils.MockModel.create(
+      responses=[function_call_no_schema, 'response1', 'response2']
+  )
+
+  tool_agent = Agent(
+      name='tool_agent',
+      model=mock_model,
+  )
+
+  root_agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      tools=[AgentTool(agent=tool_agent)],  # Default include_plugins=True
+  )
+
+  runner = testing_utils.InMemoryRunner(root_agent, plugins=[tracking_plugin])
+  runner.run('test1')
+
+  # Plugin should be called for both root_agent and tool_agent
+  assert tracking_plugin.before_agent_calls == 2
+
+
+def test_include_plugins_explicit_true():
+  """Test that plugins are propagated when include_plugins=True."""
+
+  class TrackingPlugin(BasePlugin):
+
+    def __init__(self, name: str):
+      super().__init__(name)
+      self.before_agent_calls = 0
+
+    async def before_agent_callback(self, **kwargs):
+      self.before_agent_calls += 1
+
+  tracking_plugin = TrackingPlugin(name='tracking')
+
+  mock_model = testing_utils.MockModel.create(
+      responses=[function_call_no_schema, 'response1', 'response2']
+  )
+
+  tool_agent = Agent(
+      name='tool_agent',
+      model=mock_model,
+  )
+
+  root_agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      tools=[AgentTool(agent=tool_agent, include_plugins=True)],
+  )
+
+  runner = testing_utils.InMemoryRunner(root_agent, plugins=[tracking_plugin])
+  runner.run('test1')
+
+  # Plugin should be called for both root_agent and tool_agent
+  assert tracking_plugin.before_agent_calls == 2
+
+
+def test_include_plugins_false():
+  """Test that plugins are NOT propagated when include_plugins=False."""
+
+  class TrackingPlugin(BasePlugin):
+
+    def __init__(self, name: str):
+      super().__init__(name)
+      self.before_agent_calls = 0
+
+    async def before_agent_callback(self, **kwargs):
+      self.before_agent_calls += 1
+
+  tracking_plugin = TrackingPlugin(name='tracking')
+
+  mock_model = testing_utils.MockModel.create(
+      responses=[function_call_no_schema, 'response1', 'response2']
+  )
+
+  tool_agent = Agent(
+      name='tool_agent',
+      model=mock_model,
+  )
+
+  root_agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      tools=[AgentTool(agent=tool_agent, include_plugins=False)],
+  )
+
+  runner = testing_utils.InMemoryRunner(root_agent, plugins=[tracking_plugin])
+  runner.run('test1')
+
+  # Plugin should only be called for root_agent, not tool_agent
+  assert tracking_plugin.before_agent_calls == 1