I mean, invalidating of the "observable" chain could also be done in JS, but I don't think that I know of other languages that could automatically transfer the state to the client.

Ruby(!) supports them, so it might be possible for Rails to create something like the pattern I mentioned. In fact, Ruby people use continuations for a few things like the built-in Generator class and making "restartable exceptions" so the thrower can figure out how to deal with the problem rather than the catcher, which is sometimes quite useful: http://chneukirchen.org/blog/archive/2005/03/restartable-exc...

Properly implementing continuations is a huge implementiation burden though, which is another reason why the're uncommon. The language would have to make the stack frame itself slicable and serializable, and it's hard to get good performance when the call stack itself becomes a "first class" language construct. Consider a duplicate() function that saves the state of a program and then spawns ten threads that each reload that state! Have fun implementing continuations in a way that supports that, Guido! :)