A rotated frame's guides run along its own axes and span only the frame
(drawn, hit-tested and dragged along them, with a cursor that follows the
line); a guide dropped from a ruler onto a turned frame converts the page
point into the frame's coordinates, along its axis nearer the ruler's.
Layers inside a rotated frame snap in its space: to its guides, edges,
layout grids and siblings along its axes, keeping whole pixels there.
New engine module `guides` (segment, offset_at, frame_axis, line_in);
measuring finds quarter-turned frames' guides too.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
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