OptionalattachmentsStaff member's name on staff messages, otherwise null.
OptionalcardsCards shown with this (assistant) message.
May be empty: an assistant message can carry only cards, a user message only photos.
OptionalrepliesShort replies the assistant suggests, in the shopper's language. Only on the last message,
only from the assistant, and only while it answers (status bot). Show them as buttons that
send the text as the shopper's next message.
Photos the shopper sent with this (user) message.