Waiting for a late page in the background nudged the queue every half
second, which resets its own retry backoff while offline, and kept
polling after the provider was disposed. The background wait now only
watches, less often, and stops on dispose. The existing page-add test
now expects "+" to wait out its window when the server answers nothing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>