feat(policy): resolve scheduling participant privacy

docs/POLICY_DECISION_PROVENANCE.md

@@ -20,6 +20,34 @@ When retention needs audit-log storage behavior, it requests the
 `audit.retention` capability; it does not import audit module tables or
 providers directly.
 
+## Scheduling Participant Privacy
+
+Policy exposes `policy.schedulingParticipantPrivacy` as an optional restriction
+hook. Scheduling supplies the request-level visibility choice and remains
+responsible for its secure fallback when Policy is absent. The provider never
+broadens that choice.
+
+System and tenant settings may contain:
+
+```json
+{
+  "scheduling_participant_privacy_policy": {
+    "maximum_visibility": "aggregates_only"
+  }
+}
+```
+
+`maximum_visibility` is either `aggregates_only` or `names_and_statuses`.
+Omitted settings impose no additional restriction. Effective visibility is the
+most restrictive of the Scheduling request, the system ceiling, and the tenant
+ceiling. Explicit malformed policy fails closed to `aggregates_only` and is
+reported in decision details without echoing the invalid stored value. Policy
+sources include only explicitly configured or invalid system and tenant steps.
+
+The current slice is resolver-only. A managed write API and administration UI
+must add validation, audit, parent-ceiling enforcement, and configuration
+safety registration before operators can edit this setting through GovOPlaN.
+
 ## Backend DTOs
 
 Use `govoplan_core.core.policy.PolicyDecision` for explainable policy results: