Chain verdict

the verdict of one combination's whole chain, checked in this order: VALIDATED when the expensive tier ran to completion with at least one survivor; KILLED_EXPENSIVE when it ran and left none; KILLED_KFOLD when the K-fold ran to completion with no pass and the expensive tier was never entered; KILLED_HOLDOUT when candidates cleared the cost and sample gates and none cleared the out-of-sample floor; KILLED_AT_GATES when the cost and sample gates killed every candidate; INTERRUPTED when the chain stopped before a verdict (a stop, a stage cut off, a route the later stages cannot drive)