Metric validity

Metrics are evaluated per scenario and category. Current-belief and authority metrics use five scenario rows per category. Historical metrics use only rows with an expected historical answer. Promotion, erasure, temporal, and evidence-family metrics return not_applicable when their applicability denominator is zero; they do not award a perfect score for an empty strategy. Rates are never inferred from prose. Privacy leakage counts a violation only when a record is promoted outside its permitted scope. Abstention is evaluated against an explicitly expected ambiguity decision.