Seed sidebar default pages lazily on expansion, scope page-tab dedupe
to the target pane, let a sole tab split its own pane with a factory
backfill, close menus when focus enters a sandboxed iframe, and pin the
code preview copy banner while unifying its background with the pane.
Chip capsules with scroll fades and live titles, drop-zone hint cards, the
canCloseTab control policy with the quiet lone chip and self-dismissing empty
menu, and a room reading that stays independent of hidden split controls.
imccyu