How this demos upstream drift

Each carrier is a separate mock in /mocks/<name>/. Each ships a small library of named drift recipes (rename a field, require a header, change a type, remove an endpoint…). Applying one introduces a real schema change that Fastify enforces. The gateway's adapter call fails with a clear validation error; the other carrier's column keeps rendering. This is exactly the "one partner drifted, fix just that adapter" story customers see in production.