Spline without bug

https://observablehq.com/@christophe-yamahata/spline-editor-without-bug

Spline Editor / Splice: Insert control points between existing ones

https://observablehq.com/@christophe-yamahata/spline-editor-splice-insert

Draggable axis with arrow

https://observablehq.com/@christophe-yamahata/draggable-axis-with-arrow?collection=@christophe-yamahata/curves