A clean sheet proves little on its own: how much a failure erases sets the sample cost of certifying agent risk
Dangerous-capability evaluations often use the milestone method: split a multi-step task into ordered milestones, run the agent a few times from prepared states, and record a clean sheet if every run fails. A new analysis partitions the task into checkpoint segments, encodes how much progress a failure erases through the reset rule, and shows that counting possible completion windows yields a bound on completion probability for any specified attempt budget. In rare-risk phase interiors, the minimum expected number of zero responses is governed by the mean length of active segments, and every asymptotically optimal audit must divide its responses equally among active milestones.