What building cross-service RBAC taught me about the difference between a fast check and a correct one

VaultPay is a wallet microservice I built on top of AuthShield.

Previous parts:

Part 1 is here: I Built AuthShield and Immediately Knew It Wasn't Enough

Part 2 is here: The Silent Failure I Never Saw Coming: What VaultPay Taught Me About Consistency Under Failure