ResizableDirective started a drag from offsetWidth, which includes
padding and border, but writes the result to style.width. The hosts
are content-box, so the first move widened a padded host by its
padding plus border: 23px on the workspace categories panel, 1px on
the Favorites sidebar. Each drag also saved a width that much larger.
A drag now starts from the computed CSS width (the box style.width
sizes), falling back to the directive's own width when that is not a
length. Border-box hosts (live-layout and groups rails) are unchanged.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>