* feat(scene-graph)!: make a stroke a paint
Stroke extends Fill, so a stroke carries the same paint vocabulary a
fill does instead of a lone color. Every construction site now states
a solid paint type, which keeps today's behaviour exactly; rendering,
.fig conversion, and the stroke panel still read solid strokes only.
copyFill is generic over the paint shape so copyStroke reuses it
rather than repeating the deep copy of gradient stops, transforms and
pattern fields.
Groundwork for the gradient and image strokes in #797.
* test(scene-graph): cover a stroke's nested paint data in copyStroke
A stroke is a paint now, so its gradient stops and transform must copy
as deeply as a fill's; the fixture was solid and proved only the color
and dash pattern.
ARROW_LINES and ARROW_EQUILATERAL stroke caps were accepted by the schema
and round-tripped from .fig files, but the renderer mapped every cap to
Butt, so imported arrows lost their heads and arrows could not be drawn
locally.
Add a pure arrow-cap geometry module to scene-graph (open-endpoint
collection with per-vertex cap overrides, weight-scaled head geometry)
and draw heads in the stroke color for LINE nodes and open VECTOR
centerline strokes, including the dashed-centerline path. Fold the head
reach into strokeOverflow and the node picture margin so heads are not
cropped by visual bounds, caches, or culling. Round-trip per-vertex
stroke caps through the .fig vector style override table so one-ended
Figma arrows import correctly. Expose both caps in the stroke inspector
cap picker with localized labels, and cover the renderer with an
arrow-stroke-caps Playwright canvas snapshot.
Claude-Session: https://claude.ai/code/session_012zjEbyLSBYyPpJP4fu1XNB
