One ledger, two chains — what I learned about multi-chain payment architecture from a reader's correction

In the previous post in this series I wrote about Base as the payment rail for QuackBuilds, and made an argument about why card-network economics break for certain payment shapes that onchain rails handle natively. The post landed cleanly enough on its own, but a reader’s correction in the comments — and a follow-up post on his own blog — opened up a deeper architectural question that I wasn’t ready to answer at the time and am still not ready to answer now. This post is what I learned from the