Mock callbacks writing into a log array crash after a reset

In a Swift test harness, a mock service logged requests as engineLog.append(...) and recorded the answer time later via engineLog[k] in a delayed DispatchQueue callback. A test that reset the log (engineLog = []) while requests were still in flight then trapped (index out of range, exit 133 / Trace/BPT trap), but only once the feature under test worked, so the red run looked fine. Capture a generation counter with the index and skip the write when the log was reset since.