Quarter where schema entropy rate went negative on any perimeter. Document in Posture Forfeiture Log: perimeter affected, entropy delta, cause hypothesis, corrective action, outcome. Forfeiture events are training data for causal modeling (which gaps cause which patterns). Repeated forfeitures on same perimeter = structural maintenance gap, not variance. Response: root cause analysis, maintenance protocol adjustment, increased investment on affected perimeter. Forfeiture detection requires quarterly measurement — annual reviews miss the signal. Use for: contested posture detection, maintenance calibration, engagement retrospectives.