Text Chat

Stateless text-chat endpoint for ChaCha check-in calls.

The frontend posts the full conversation history each turn (along with mode = a1_intent | a2plus_orient | wrapup | followup_d2) and gets back ChaCha's next message. When ChaCha emits a final JSON summary, the endpoint sets done=true and the frontend marks the matching checklist item complete (only for a1_intent / a2plus_orient — wrapup and followup_d2 use celebrate-seen / followup-d2-seen instead).

This intentionally reuses the same prompt builders the voice path uses, so the conversation goal is identical: placement signal + intent capture for orient, congrats+feedback for wrapup, etc.