feat: add a2a liteagent, auth, transport negotiation, and file support

* feat: add server-side auth schemes and protocol extensions

- add server auth scheme base class and implementations (api key, bearer token, basic/digest auth, mtls)
- add server-side extension system for a2a protocol extensions
- add extensions middleware for x-a2a-extensions header management
- add extension validation and registry utilities
- enhance auth utilities with server-side support
- add async intercept method to match client call interceptor protocol
- fix type_checking import to resolve mypy errors with a2aconfig

* feat: add transport negotiation and content type handling

- add transport negotiation logic with fallback support
- add content type parser and encoder utilities
- add transport configuration models (client and server)
- add transport types and enums
- enhance config with transport settings
- add negotiation events for transport and content type

* feat: add a2a delegation support to LiteAgent

* feat: add file input support to a2a delegation and tasks

Introduces handling of file inputs in A2A delegation flows by converting file dictionaries to protocol-compatible parts and propagating them through delegation and task execution functions. Updates include utility functions for file conversion, changes to message construction, and passing input_files through relevant APIs.

* feat: liteagent a2a delegation support to kickoff methods

lib/crewai/tests/a2a/test_a2a_integration.py

@@ -104,6 +104,7 @@ class TestA2AStreamingIntegration:
             message=test_message,
             new_messages=new_messages,
             agent_card=agent_card,
+            endpoint=agent_card.url,
         )
 
         assert isinstance(result, dict)
@@ -225,6 +226,7 @@ class TestA2APushNotificationHandler:
             result_store=mock_store,
             polling_timeout=30.0,
             polling_interval=1.0,
+            endpoint=mock_agent_card.url,
         )
 
         mock_store.wait_for_result.assert_called_once_with(
@@ -287,6 +289,7 @@ class TestA2APushNotificationHandler:
             result_store=mock_store,
             polling_timeout=5.0,
             polling_interval=0.5,
+            endpoint=mock_agent_card.url,
         )
 
         assert result["status"] == TaskState.failed
@@ -317,6 +320,7 @@ class TestA2APushNotificationHandler:
             message=test_msg,
             new_messages=new_messages,
             agent_card=mock_agent_card,
+            endpoint=mock_agent_card.url,
         )
 
         assert result["status"] == TaskState.failed

lib/crewai/tests/a2a/utils/test_task.py

@@ -43,6 +43,7 @@ def mock_context() -> MagicMock:
     context.context_id = "test-context-456"
     context.get_user_input.return_value = "Test user message"
     context.message = MagicMock(spec=Message)
+    context.message.parts = []
     context.current_task = None
     return context