But don't they update DNS so that the origin for the (presumably sub) domain is now pointing at your localhost? Perhaps the solution is to track the DNS state.

But don't they update DNS so that the origin for the (presumably sub) domain is now pointing at your localhost? Perhaps the solution is to track the DNS state. Any external to localhost changes should be blocked. And any communication between parent/sub domains should never cross the localhost boundary no matter what DNS might say. Of course this would interfere with development so it would need to be something you could toggle. But I'm 100% sure there's something I haven't thought of that depends on this behavior.