Full round trip decompilation <--> compilation between Observable runtime and my in-notebook editor is working. I've put a CodeMirror UI on it and smooshed it into a single cell for easy import. works on mobile. A few areas are broken: imports, anonymous cell editing and adding variables. Note I am sticking to Observablehq flavoured JS, but it could support any language if you have a compile to JS for it.

I don't quite get what I'm looking at. Is this not running at observablehq.com?

It is an observable cell running inside observable that can edit other cells in the notebook without going through Observable's editing interface. ie.. if I export the enclosing notebook, it retains this editor. Its like Obseservable, but implemented in userspace. Sorta pointless if all you want to do is use Observbalehq notebooks in the expected workflow, but quite powerful if you want to edit off platform (if there was a method to persist the results), or do program synthesis (its scriptable). Thats the plan anyway, still a WIP (hence only a devlog entry)