vellum 0.6.3

One bug, in two halves, found while wiring keyed data-label backgrounds in vellumplot.

A keyed roundrect_grob() was broken twice over

roundrect_grob() is a batch — one rounded box per (x, y, width, height, r) element — but it was treated as a single shape on both sides of the seam:

• It recycled key/meta to length 1, so roundrect_grob(key = c("a", "b")) silently kept only "a".
• scene_model() classed roundrect as a single shape (one row per grob), so a grob drawing N keyed boxes reported one element against the backend's N and aborted on the element-count check.

Roundrect is now a keyed batch, like text_grob(): each keyed box is one scene_model() row carrying its own key and meta, and an unkeyed roundrect stays out of the model entirely.

Rendering is unaffected — scene_model() is interactivity metadata only.

Note

This is the first bug in this series found by using the engine from vellumplot rather than by testing it in isolation — which is exactly what the downstream integration pass was expected to surface.