Tracing bad funds through shielded pools

A proposed design would let note owners in shielded token pools learn how much of their balance descends from a publicly blacklisted deposit, without revealing anything else. Each note would carry encrypted records of its upstream deposits, so the owner could learn the amount that flowed from a flagged deposit and then use a "decontamination circuit" to create a clean note. The proposal is motivated by Railgun's one-hour deposit delay, which the text says a bad actor could slip past, and by Payy, which removes nullifiers and therefore makes its whole transaction graph observable. It is presented as an exploration, not a recommendation.