Resize an auto-fill grid and the cells jump. You drag the viewport, a track's worth of items slides across, and there are no in-between frames. Nothing to transition. Grid cells are virtual — the tracks get computed, but the cells themselves aren't boxes the layout engine can interpolate a position on. That's the wall.
The bram.us demo walks around it with CSS anchor positioning and a plain transition on inset. No JavaScript. No View Transitions. Interruptible.
The wrapper you'd normally delete
You need a real box to anchor. So each cell gets one, and the visible content lives inside it as an absolutely-positioned child:
<div class="grid">
