A lineage as rekeyByLineage consumes it: the entries, plus the
base-revision keys the diff left DELETED with no lineage at all. The two
together let a rekey tell an unchanged key (no entry, not deleted: the row
keeps its key) from a deleted one (orphaned). Without deleted, a key with
no entry is passed through unchanged — losing a row is the worse failure.
A lineage as rekeyByLineage consumes it: the entries, plus the base-revision keys the diff left DELETED with no lineage at all. The two together let a rekey tell an unchanged key (no entry, not deleted: the row keeps its key) from a deleted one (orphaned). Without
deleted, a key with no entry is passed through unchanged — losing a row is the worse failure.