What's the privacy violation risk here? A doesn't learn anything through those prefetches about whether or not the user has previously cached any B resources (b

What's the privacy violation risk here? A doesn't learn anything through those prefetches about whether or not the user has previously cached any B resources (because A never sees the timing or result of its prefetch requests - it doesn't even know if the browser attempted them). B obviously knows what resources A prefetched because they were requested from B in the first place. And if A wants to pass information to B, they don't need to do a complex prefetch dance, they can just load an img src. So I don't see any way for A or B to learn anything about the user's behavior on one another's site without the other site's cooperation?