Function decode_legacy_decision_audit 

pub fn decode_legacy_decision_audit(
    config: &DecisionAuditConfig,
    paged: &PagedEvent,
) -> Result<LegacyAuditEntry, LegacyDecisionAuditDecodeError>

Decodes a historical Gatekeep audit event without treating it as current.

The returned LegacyAuditEntry retains the pre-4.0 optional fields and must be explicitly mapped by migration code before it can reach an gatekeep::AuditSink.

Errors

Returns LegacyDecisionAuditDecodeError when event attributes, payload identity, or tenant routing do not match the historical contract.