When the sidebar toggled, the header's toggle mounted/unmounted in a
single frame, so its 48px footprint (button + gap) popped and dragged
the title and chips sideways while the sidebar was still mid-slide —
'kind of masked by the motion, but very much noticeable.'
The toggle is now ALWAYS MOUNTED, owning a slot whose width+margin
animate in lockstep with the sidebar's own width transition (same
duration-200, same easing, both gated on mount so no load flash):
- when open the slot is exactly ZERO (w-0 with -mr-3 cancelling the
header's gap-3) — resting layouts are pixel-identical to the old
conditional render;
- the icon fades with the slot (opacity in the same 200ms) and is
clipped by it as the slot collapses — no popping in either direction;
hidden state is pointer-events-none, aria-hidden, tabIndex -1;
- the mount-gating rule grows to transition-[width,margin,opacity].
rAF-verified both directions: the title's x-path is monotone from
frame one (old bug teleported 48px in one frame; the margin blip
caught on the way is also gone), icon opacity eases 0.12→1 over the
slide. Gates: typecheck, lint, 469/469.
amosblomqvist
64c644f42c