Scene → SVG generator. The shared intermediate representation: the editor preview and (later) the PNG rasterizer both consume this output, so what you edit is what renders.

Pure and deterministic — render/3 is a function of (scene, values). All user-authored strings are XML-escaped, and canvas dimensions are clamped as an OOM guard.

Text word-wraps to its box width using a character-count estimate (~0.55em, matching og), honors explicit \n breaks, and vertically aligns via valign. This estimate is a Phase-2 stepping stone; measurement-accurate wrap (same wrap points as the rasterizer paints) lands with the font stack in a later phase. Anchor reflow and button auto-width are likewise later — this generator lays out by explicit boxes.