chore: remove legacy validation that forbids co-exist of agent transfer and output_schema. Closes #3318

Remove validation for output_schema and agent transfer flags.

The check that prevented `output_schema` from co-existing with agent transfer capabilities (`disallow_transfer_to_parent` or `disallow_transfer_to_peers` being False) has been removed. The agent will no longer automatically set these transfer flags to True when `output_schema` is present.

Co-authored-by: Ieva Grublyte <ievagrublyte@google.com>
PiperOrigin-RevId: 825998224

tests/unittests/flows/llm_flows/test_output_schema_processor.py

@@ -72,6 +72,24 @@ async def test_output_schema_with_tools_validation_removed():
   assert len(agent.tools) == 1
 
 
+@pytest.mark.asyncio
+async def test_output_schema_with_sub_agents():
+  """Test that LlmAgent now allows output_schema with sub_agents."""
+  sub_agent = LlmAgent(
+      name='sub_agent',
+      model='gemini-1.5-flash',
+  )
+  agent = LlmAgent(
+      name='test_agent',
+      model='gemini-1.5-flash',
+      output_schema=PersonSchema,
+      sub_agents=[sub_agent],
+  )
+
+  assert agent.output_schema == PersonSchema
+  assert len(agent.sub_agents) == 1
+
+
 @pytest.mark.asyncio
 async def test_basic_processor_skips_output_schema_with_tools():
   """Test that basic processor doesn't set output_schema when tools are present."""