nx_sketch_zscore.nx

sketch_zscore.nx -- point z-score anomaly detector. Composes against sketch_stream_stats (running mean + stddev) to flag individual samples deviating from the streaming baseline: z = (x - mean) / stddev alarm if |z| > threshold (typical 2.0 ~ 95% conf, 3.0 ~ 99.7%) CAPABILITY: - O(1) state (mean + variance from StreamStats) - online: baseline updates with every sample - Returns Z in PPM ([-1e10, +1e10] practical range) - Sealed verdict: NORMAL / HIGH / LOW COMPLEMENTS THE ANOMALY FAMILY: - sketch_cusum cumulative shift over a window - sketch_mann_kendall monotonic trend test - sketch_zscore (this) point outlier vs running baseline CONFIGURATION: "warm-up" period: do not raise alarms until count >= min_count. Default: min_count = 30 (statistician's rule-of-thumb for CLT). LOSSLESS-LANGUAGE DISCIPLINE: returns z in PPM with NX_ENV_ABS, param_a = 1 (PPM quantization). Production tier; exact integer arithmetic over the running statistics.