This looks awesome! I've been working on a fairly similar project but just for myself (definitely not production ready) and this format for interacting with code seems like it has a lot of potential. One thing I was considering as a value-add was that this type of interface enables is having support for MDX output or even embedded MCP UI apps in the middle of a chat. Typical CLI agents don't support that but a UI that lets your code embed Excalidraw diagrams and graphs could be great for things like data analysis on the go. Even embedding images in a chat would make using coding agents a lot nicer imo.