Port the OMP usage poller into the Pi provider so context/token usage updates during active turns instead of only at completion. - Add PiUsagePoller with 3s throttle, dedup, and generation-based cancellation - Wire poller into PiRpcAgentSession turn lifecycle - Add unit tests for polling, dedup, error handling, and turn completion Co-authored-by: Slava Goltser <slavikg@gmail.com>