With the guard enabled the binary search recovers best sampling_u=0.078125 (rate 2.30 req/s), identical to the full-replay baseline. The guard fired on exactly the one feasibility-knee probe (0.08594, re-measured full -> infeasible); the other three probes truncated to ~45-50%. Net ~38% replay saved on the trial with no peak-rate overestimate. Stop-A + boundary guard is safe to enable. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>