Replace _poll_task for one-shot tasks with _poll_oneshot, which uses two
phases: (1) a burst of up to 11 immediate polls at 50ms intervals to catch
tasks that complete in <500ms, and (2) exponential-backoff polling once
finished=False is observed. A 599 during burst → window missed (fail fast).
A 599 during Phase 2 (task was seen running) → same. _poll_task is
simplified back to a plain long-poll with no window_timeout logic.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
marcus
0e8ffaa6df