The pane waited 150 ms on hover and 60 ms on a keyboard step before
following the sidebar highlight, so every preview paid for the fast walk
it might have been. Replace both with a leading-edge 120 ms gap: the
first move shows at once, a burst is coalesced to its start and its end.
The row's own hover no longer eases either — `background` was on a 120 ms
transition, which is what read as lag on the row itself.
The sidebar also rebuilt its whole tree on every `SessionUpdated`, a
couple of times a minute per live session, dropping `:hover` from the row
under the pointer. Refreshes that change nothing structural now patch the
activity rail and meta line into the standing rows instead.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
