Carets, selections, presses and the input method box measured the line as columns times one 'm', so a wide character (CJK, emoji) put the caret mid-glyph. editor::measure lays out the drawn line; rulers and indent guides stay on the column grid; whitespace marks hide the rest. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>