Backend: _get_chat_history() reads JSONL sessions. API: GET /api/agents/{id}/chat-history. Frontend: Chat History tab shows session list with title, model, message count. Click to open session in chat panel.
Backend: _log_agent_activity, _get_activity_log, _get_error_log. API: GET /api/agents/{id}/activity and /errors. Frontend: Activity and Errors tabs in agent detail overlay. CSS: activity-event-row, error-event-row. Config fix: Z.ai API key.