- TREE THREADS: open folders and chains drop a vertical guide from
their expander arrow straight down through their children — at the
arrow's own column (37px clusters / 73px chains), subtle border/50.
Live-measured pixel-exact: arrow center = thread x (325=325, 361=361).
- The framed table: a rule under the header and under the last group
join the between-group separators; rows stay lineless.