I'm working on writing a sort of code and data playground from scratch - with currently only CodeMirror, ProseMirror, and some icons as dependencies - so that everything in it can be edited live. Everything is web components with the shadow DOM. It is sandboxed both as a whole and at the notebook level. The overall sandboxing uses a Content Security Policy that allows inspecting the URL for following a link, to enable using untrusted code (from humans or an AI) and private data without it easily being leaked. I've built a resizable split view, draggable tabs with multiple panes, and a color picker. It's a few dozen Markdown files with code in fenced code blocks and a Deno and Docker-based build process. There is a hybrid notebook/playground editor with the fenced code blocks changed into links that open the files in tabs. It's open source and at https://ristretto.codeberg.page/