The usual shimmer paints a wide gradient and animates background-position. That repaints the element every frame.

GodUI paints the gradient once. It lives on an ::after layer that covers the block, and the layer starts one full width to the left (-translate-x-full), fully outside it. The animation moves it to one full width to the right, so the band enters through the left edge and leaves through the right (under dir="rtl" the loop plays in reverse, right to left; the curve is symmetric, so it eases the same way). The block is overflow-hidden, which clips whatever is outside it. Only translate changes, so the layer is promoted once and the compositor slides it.

The band is foreground at 6% opacity on the accent fill, which keeps it readable in both themes without turning the placeholder into a flash. This scene slows the loop to 3s so you can follow it.

A sweeping band is still movement across the whole block. For prefers-reduced-motion, motion-reduce:after:hidden removes the band and motion-reduce:animate-pulse puts back shadcn's original fade: no travel, just an opacity change. The scene shows that pulse.

Each block carries its own band and runs the same 1.6s loop from the moment it mounts. Blocks that mount together stay in step; one that mounts later runs the same loop, offset by when it arrived.