Janet's REPL has a debug mode, but I'm sadly not qualified to evaluate whether/how it measures up to CL's due to my own inexperience with either. :)

As for restarts (I had to Google around to get an idea of what that means)—it seems to me that Janet does not have first-class support for restarts in the way that some other Lisps, for e.g. CL, do. Presumably (as it would be in most other languages I would suppose) one could recreate that experience in Janet by tapping into the first-party error handling and REPL primitives. But you'd definitely be rolling your own rather than having it already in Janet out of the box.