`layout_.axes` reached the viewport's right edge, so the rightmost x tick label -- centred on its tick -- had half of itself outside the plot, and the newest sample's ink landed on the frame. `Plot::set_right_gutter()` reserves a band there, out of the same `1 - kMinAxesShare` allowance the label and title strips are served from, so it can no more squeeze `axes` below the half-viewport floor than they can. `Figure` sets one value on every row, the left gutter's reason: the rows' axes have to end on a common column as well as start on one. Nothing is drawn in the band, so unlike the strips it is a want and never a measurement: no measuring pass, and it cannot feed the layout's fixed point. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>