feat: Pass event id as a metadata when it is converted into a message

PiperOrigin-RevId: 860929058

src/google/adk/a2a/converters/event_converter.py

@@ -131,6 +131,7 @@ def _get_context_metadata(
         _get_adk_metadata_key("session_id"): invocation_context.session.id,
         _get_adk_metadata_key("invocation_id"): event.invocation_id,
         _get_adk_metadata_key("author"): event.author,
+        _get_adk_metadata_key("event_id"): event.id,
     }
 
     # Add optional metadata fields if present
@@ -479,7 +480,6 @@ def _create_status_update_event(
     task_id: Optional task ID to use for generated events.
     context_id: Optional Context ID to use for generated events.
 
-
   Returns:
     A TaskStatusUpdateEvent with RUNNING state.
   """

tests/unittests/a2a/converters/test_event_converter.py

@@ -56,6 +56,7 @@ class TestEventConverter:
     self.mock_invocation_context.artifact_service = self.mock_artifact_service
 
     self.mock_event = Mock(spec=Event)
+    self.mock_event.id = None
     self.mock_event.invocation_id = "test-invocation-id"
     self.mock_event.author = "test-author"
     self.mock_event.branch = None
@@ -130,6 +131,7 @@ class TestEventConverter:
         f"{ADK_METADATA_KEY_PREFIX}session_id",
         f"{ADK_METADATA_KEY_PREFIX}invocation_id",
         f"{ADK_METADATA_KEY_PREFIX}author",
+        f"{ADK_METADATA_KEY_PREFIX}event_id",
     ]
 
     for key in expected_keys: