The backend switched from CL -> Nodejs, the frontend switched from JS -> Rust core bundled with JS ui.

There was an experimental app core written in CL (https://github.com/turtl/core-cl) that is basically the precursor to what the rust core is today. I did have success embedding lisp (via ECL) into other components (like node-webkit at the time) but ultimately it was kind of an uphill battle, as with many off-the-beaten-path things in common lisp.