if not errors:
            # Shared serializer for stream items (JSONL and SSE).
            # Validates against stream_item_field when set, then
            # serializes to JSON bytes.
            def _serialize_data(data: Any) -> bytes:
                if stream_item_field:
                    value, errors_ = stream_item_field.validate(
                        data, {}, loc=("response",)
                    )

                if route.is_json_stream:
                    jsonl_content: dict[str, Any] = {}
                    if route.stream_item_field:
                        item_schema = get_schema_from_model_field(
                            field=route.stream_item_field,
                            model_name_map=model_name_map,
                            field_mapping=field_mapping,