Can you not design a PoW that is most efficient in a browser? Don't brute force hashes like Hashcash/Bitcoin, do something similar to RandomX instead but in JS. Browsers ought to run the fastest JS interpreters already so if interpreting JS becomes the bulk of the work, that attack might not work. Maybe even involve the DOM or whatever else makes sense.
No no no. You don’t realise the compiled intermediate can be _trivially_ reused for every request, and identified by the hash of the JavaScript code. Browsers already do this, it’s just your attacker has a bigger cache, and not by a little bit.
Browsers _intentionally_ limit the amount of memory and cpu cycles a tab can consume to make for a nicer human experience.
