Is there anyway to write to/read from the saved instance state from a Compose function - like some kind of ambient or something that provides hooks for that?

Not currently. There's not exactly a single saved instance state - `View`s have their own, `Fragment`s have their own, `Activity`s have their own... you could easily create the `Ambient`s yourself and wrap your content in them (or just pass it in as a parameter, depending on what you're doing).

It's likely going to be based on the incoming ViewModel/SavedStateHandle stuff coming into arch components