sketch_cusum_vs_threshold_bench.nx

sketch_cusum_vs_threshold_bench.nx -- change-point detection bench. CLAIM TO VALIDATE: CUSUM (Page 1954) detects a SHIFT in stream mean faster and with fewer false alarms than a single-threshold rule. Threshold-only alerts when ANY sample crosses the threshold -- prone to false positives from natural noise. CUSUM accumulates evidence over multiple samples, so it triggers only on persistent drift. WORKLOAD: - Phase 1 (steps 1..100): samples ~ N(100, 5) -- normal regime - Phase 2 (steps 101..200): samples ~ N(120, 5) -- shifted mean Threshold = 115 (between the two means). MEASUREMENT: CUSUM: count detections in Phase 1 (false alarms) vs Phase 2. Threshold: same. Score = (correct detections in Phase 2) - (false alarms in Phase 1). Higher wins.