Use when the user wants to roll back a change by moving a Unit's head (or a set of Units' heads) to a prior revision — phrases like "roll back this change", "revert the last release", "undo the ChangeSet", "restore to the last applied revision", "back out yesterday's image bump", "put the head back where it was before this ChangeSet", "roll back the promotion". Always rolls back by moving head via `cub unit update --restore <target>` against one Unit or a Filter-scoped set (optionally tagged), then hands off to the `cub-apply` skill to push the restored state. Do not load for drift between ConfigHub and cluster (use `drift-reconcile`) or for rolling back a single-field change where a forward mutation via `cub-mutate` is clearer.