Fuzz steps can move the clock backwards, while a peer's idle time counts from its last frame, so advancing from the current tick could stay short of the idle window. Track the latest tick and probe from it; skip the probe when the tick is too close to u64::MAX to advance. A 5-minute nightly run (84k inputs) is clean after the fix. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>