Tightly-fitted text stops breaking a word early

A precision fix for text laid out at exactly its own width - the packed links in a site's top bar, a button's label, a compact menu. A rounding difference could make such a line break its last word onto a second row even though it fit, which then pushed the whole bar taller and nudged everything below it. The engine now measures that last-word fit the way the reference browser does, so snug text stays on one line and headers keep their intended height.