- The three panel modes were three separate fixed-width asides, so a
mode switch jumped the whole transcript column width in one frame:
scrollbar flash, overshoot, re-correct. Now ONE aside animates its
width exactly like the left sidebar (reusing the sidebar-motion
hook, so it inherits the provider's mount-gated transition), with
a FIXED-width inner layer clipped by overflow-hidden — content
never reflows mid-transition.
- The chat header was auto-height: the sidebar toggle (a size-9 icon
button) renders only while the sidebar is closed, so opening it
collapsed the row and slid the title + phase chip up. The header is
now a constant h-10.