Function complete_staged_apply 

pub async fn complete_staged_apply(
    staged: StagedQuickstartApply,
) -> Result<QuickstartApplyOutcome, Vec<QuickstartError>>

Persist one staged quickstart and install its personality files without a publication domain. A persistence failure returns with nothing committed; a personality failure returns QuickstartApplyOutcome::CommittedWithSideEffectErrors because the config is already on disk.