[AsPulse]

The vector DecoratedBox reported only its own box as its paint bounds, which cuts an overflowing child while the box is the rasterization root but not once the box sits inside another vector container: a vector parent keeps its children's nodes and drops their view boxes, so the child's overflow simply paints on. The raster variant clips in either position, because it composites the child into a box-sized buffer. Separately, the vector variant's own border strokes the box outline, so half its width falls outside the box — and was cut off, the same omission #84 fixed for path shapes.

Change

• Wrap an overflowing child in a ClipGroup at the box, so a DecoratedBox clips wherever it appears; a child that already fits emits the same node tree as before.
• Include a visible border's conservative stroke outset in paint_bounds and render().view_box, since the border is the box's own paint rather than the child's.
• Share rect_path_commands with Clip instead of rebuilding the box path.
• Add unit coverage for the clip, the no-clip fast path, and the border outset, plus CPU rasterization regressions for a nested box cutting its child and for a border keeping its outer half.
• Update the English and Japanese layout tutorials, which described the clip as raster-only.
• Add a major changeset because the corrected clip and bounds can change existing rendered video pixels.