It is a time-sharing system where you can log in and use a programming language.

We have had those since not long after the dawn of computing.

Since at least 1970, we also had smart terminals that allowed the user to fill in a form, and validate it, before sending it to the host.

So the time-sharing session being carried out by a protocol between the web front end and back-end is not ipso facto original.

Needless to say, neither is the idea of a repl running in a separate process that provides editing, with expressions sent out to a running image for evaluation.