flushNow exits early when the queue is empty, so after ops hit max attempts
the chip pinned on "needs attention" with a Retry that did nothing — retry
now clears the stale error via a guarded clearStaleError() on the op queue.
Throttled conflict batches are now held and announced when the throttle
window expires instead of being silently consumed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>