Chats and messages

Chats and messages — contract and behavior

• The Linq-compatible surface includes chat creation and message-send operations with Wisent extensions where the product exceeds Linq.
• The router persists the selected backend and worker affinity with the chat so later sends do not drift to another physical state holder.
• Backend responses normalize into common Pydantic models before persistence and webhook emission.
• Chat identifiers are native to Most and are not interchangeable with legacy Linq identifiers during rollback.