There is no way to design such a system that is not cheatable. At the very least, someone could simply type out text from another window or device. On any normal operating system or browser, the user will be able to bypass whatever mechanism you have in place anyway.

For everyone pointing out that this idea can be cheated by just typing AI-generated text into the editor - add an AI-detector to the editor. Gamify the whole thing by making a leaderboard of people with the lowest AI-detector-similarity score across things that they have "written"

In a class setting, maybe make the AI-detection an element of take-home assignments - whoever gets the lowest AI-similarity score gets a few points of extra credit or something

As for computer science courses, I'm guessing it's hard to not write simple code that appears AI-generated...so maybe that kind of work needs a written summary to go along with the code as well

You can still just type the Ai response. Often when I generate larger code I type it instead of copy paste, that helps me understand it and spot issues faster

Can't a raspberry pi (or similar) emulate a USB keyboard? Feed it any text and the key strokes will look real to your editor.

I guess you could require a special encrypted keyboard in your plan.

We're going to invent kernel level anticheat for text editors rather than just do in person exams.