The legacy stdDev < stdDev*2 was always true. New behaviour: stdDev <= config.calibration.stabilityThreshold OR stdDev === 0. Default threshold 0.01 in scaling-units. Schema field + editor UI added. 4 BUG-PRESERVED tests rewritten + 4 new edge tests. 101/101 pass. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>