I used a "modern" app written in Cincom Smalltalk this year (still maintain and sold a high price), and you don't see the underlying system. Like you don't see the source code when opening any other app, in fact. The app resets the state at startup, so no lingering eternal session.

It's funny because in the past I got the chance to test izware Mirai, which is written in Lisp — when the app got into a problematic state (which was often on my machine) you were sent to the REPL where you could inspect the memory and so on. It was alien to me at the time. Today I dream of having that.