Recommended way to get the state of a running app?

[walfie]

(alternate title: recommended way to do hot module replacement while persisting state?)

I'm trying to get hot module replacement working in my app during development, where I can persist the state of the app between source file edits.

The straightforward way to do this is by updating my init or main to accept an optional initial state and passing in the state from a previous reload if it exists. The issue is that there isn't a convenient way to get the current state of a running app from the "outside" (i.e., the thing that calls main).

What I'm currently doing is using the shutdown callback (which does have access to the model, and can be called from outside) to set a "global" ref, but it feels kinda hacky. An alternative I considered is using pushMsg and having a "give me the current state" message with some external channel to pass the state through, but that also feels unideal, for something that is only really used in development. Or, having each update call set some global ref.

Is there a recommended approach to doing this cleanly? Or maybe if there was a state()/getState()/whatever method that could be called on a running app