This is a sub-task of rdar://105252500 , which brings some improvements to the new attachment layout to make it closer to the target specs, especially on macOS.
<rdar://problem/106534843>
Pull request: https://github.com/WebKit/WebKit/pull/11345
Committed 261665@main (d0509c40b6a5): <https://commits.webkit.org/261665@main> Reviewed commits have been landed. Closing PR #11345 and removing active labels.