Copilot Chat

Enqueue one copilot turn as a durable Celery task and return immediately. The client attaches to GET /chat/events?turn_id=... to watch stage updates, tool results, and the final reply arrive live. Running the turn outside this request means neither a slow Anthropic response nor a mid-turn API deploy can strand the founder with "Build with copilot" silently frozen (see almanac/architecture/agents/agent-copilot.md). The only write the loop can perform is create_agent, which is server-side forced to enabled=false with a non-sending delivery mode.