Hypothesis. Sharp changes in Yang–Zhang realized volatility precede directional drift and volatility mean-reversion. Edge is a winsorized (5/95) mean against a matched baseline; significance by Welch t and Mann–Whitney U; p-values Benjamini–Hochberg corrected across each study's parameter grid; overlapping events de-duplicated before statistics. Every signal carries per-regime success counts and its own fitted forward-return distribution.