agreed. i haven't played with building signer extensions but i think it's on my list of things to do, make a signer extension built with wasm to handle signing. both its memory is opaque and nothing exported *and* it only communicates over the window namespace.
the other important thing is that the extension can be used with any web app at all, where an app with an isolated webworker running wasm only signs for that app that spawns it.
