Function merge_newest 

fn merge_newest(
    branch_rows: Vec<ReviewSummary>,
    tree_rows: Vec<ReviewSummary>,
) -> Vec<ReviewSummary>

Branch rows and seat-tree rows as one list, newest first. Review ids are uuids, so none collide across the two scopes; number is per-scope and CAN repeat, which is why the tree’s rows come with the scope note beside them.