SiteEntry gains an additive FallbackGrpcEndpoint; SiteEnumerator now picks NodeA
else NodeB as primary (a NodeB-only site is no longer skipped) and carries a
distinct NodeB as the fallback. Both GrpcPull{AuditEvents,SiteCalls} clients dial
the primary first and, on a transport fault (Unavailable/DeadlineExceeded/
Cancelled/HttpRequestException/SocketException/OperationCanceled), fail over to
NodeB once before collapsing to empty — a mapping/unexpected fault does NOT fail
over. Keeps the reconciliation loss-recovery net available during a NodeA outage.
Joseph Doherty