Get asynchronous ask job status

Standard error envelope. Stable error codes for agents: invalid_request, unauthorized, forbidden, not_found, conflict, validation_failed, rate_limited, timeout, upstream_unavailable, internal_error. Retry only 408, 425, 429, 500, 502, 503, and 504. Do not retry 400, 401, 403, 404, 409, or 422 without changing the request. For 5xx, use full-jitter exponential backoff: 500 ms initial delay, multiplier 2, cap 8 seconds, stop after 4 total attempts.