Sync GovOPlaN module state

docs/POLICY_DECISION_PROVENANCE.md

@@ -3,6 +3,16 @@
 `govoplan-policy` owns policy and retention route contributions. Core keeps the
 small shared DTOs that let policy decisions look the same across modules.
 
+Privacy retention implementation lives in this module at
+`govoplan_policy.backend.retention`. It is also exposed as the
+`policy.privacyRetention` capability so older core compatibility imports can
+dispatch to the active policy module without owning policy logic in core. Core
+does not import this implementation as a hidden fallback when policy is
+disabled.
+When retention needs audit-log storage behavior, it requests the
+`audit.retention` capability; it does not import audit module tables or
+providers directly.
+
 ## Backend DTOs
 
 Use `govoplan_core.core.policy.PolicyDecision` for explainable policy results: