true when the row has nowhere to go: deleted, or a split the policy refused.
OptionalrelationThe relation that produced the answer. unchanged means the key has no
lineage entry and is not in the lineage's deleted list, so it is
matched by key in the head revision and the row keeps it. undefined
means the key is in the deleted list.
Head-revision keys the row should now be attached to; empty when orphaned.
The base-revision key the caller asked about.