Function barrier_recovery_fold_action 

pub fn barrier_recovery_fold_action(
    kind: BarrierRecoveryRecordKind,
    value_present: bool,
    record_epoch: i64,
    pending_epoch: Option<i64>,
    epoch_already_consumed: bool,
) -> BarrierRecoveryFoldAction

Select the exact mutation for one decoded barrier-state record.

The host applies this result to the entry named by the decoded group key, in log order. A consumed epoch suppresses a later retry of its injection-start, and only a matching epoch may clear the pending injection.