VC7/27/2026, 5:14:49 AM

Both pages now share one frame: hatched ground, stacked mark and wordmark,
and a gitpanel holding the form. Moving between them clips the content in
the way the rail tooltip does, and animates the panel's height from the
outgoing page's — sign-in is ~370px and sign-up ~454px, so revealing the
content alone left the new frame at full height with an empty band under
it for the whole animation.

The rail's own enter animation moves into `use-surface-swap`, which is the
same question asked twice: did we arrive from a sibling surface, or is this
a cold load? Only the former should animate.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Parent235ea0b