Declarative chart widgets — a ~100-token JSON spec in, sealed-kernel SVG out

Notes & tips

• Reuse a stable, meaningful chart_id (coverage-trend, not chart1) — it is the handle every later patch needs.
• Arrays replace wholesale under RFC 7386, so a data update re-sends the full data array. Still far smaller than re-emitting the widget.
• For recurring shapes, prefer a named component (expand_component) over hand-authoring the same spec — expansion is server-side and validated.
• The images in the tutorial are static-SVG exports of live renders (1.9–2.6 KB each) — the same trick works for READMEs and PyPI pages.