Editing the source code of notebook dependancies reactively. This is something you can't do in Observable which is where the non-interleaved editor actually has an advantage.

OK Part II done! The userspace editor + userspace exporter playing together nicely. You can try it out here. In theory you should be able to edit, export and upload to S3 without even logging into Observable. (There is not way to manage the layout of a notebook though, thats part III, so its sorta too limited to be useful yet).