Looks like we're accounting for the subgrid margin/border/padding on the wrong edge, like due to writing-mode changes between grids.
<rdar://problem/89219210>
Created attachment 452769 [details] Patch
Comment on attachment 452769 [details] Patch Assuming the bots get another crack at this after the WebGPU breakage is cleared...
Committed r290576 (247854@main): <https://commits.webkit.org/247854@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 452769 [details].