The defquery conversion routes inter-service results through
_dto_to_dict which checked __dict__ (absent on slots dataclasses),
producing {"value": obj} instead of proper field dicts. This broke
TicketDTO deserialization in the cart app. Check __dataclass_fields__
first and use dataclasses.asdict() for correct serialization.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>