Hey, this is super interesting! We have been working on a quite similar system over the past few years at Université de Montréal. We develop and use codeBoot (https://codeboot.org) to teach introductory programming courses there. We also wrote an executable book for teaching a Cegep course (think last year of high school in the US). You can find it here (https://420-sn1.codeboot.org/) but mind you, the English version is not completed past chapter 1. The book was written in French.

Our tech stack is different but the choices we made are quite similar. Multi-tiered platform, markdown for authoring, executable exercises, teacher platform to produce, give, receive and grade homework/exams, etc. A distinguishing characteristic is that codeBoot's Python interpreter (pyinterp) allows single-stepping through the code. That's quite useful for teaching and studying.

We have a few exciting features coming up and we're working on a proper landing page and clean English translation for the book. If anybody is interested to learn more, reply here or contact me (email in my profile). I'd love to connect with educators, students or hackers alike!