[grahameb]

I'd like to be able to say, as a page / site, "disable all APIs that let this page communicate out to the net" and for that to be made known to the user.

It'd be quite handy for making and using utility pages that do data manipulation (stuff compiled to wasm, etc) safely and ethically. As a simple example, who else has pasted markdown into some random site to get HTML/... or uploaded a PNG to make a favicon or whatever.