chat.gel.assistant.message

One message in a chat, from the user or the assistant. A reply's key is the user message's key plus '.r' and the attempt number, such as '.r0' or '.r1'. The app creates the reply with status 'pending' and no content, it fills it in when generation ends. Creating fails if the key is taken, so each attempt gets exactly one reply. Sort replies by attempt number rather than by key, since '.r10' sorts before '.r2'.