A 200 is not done: make the AI walk the business scenario
The create call returned 200, the detail view 404s, and cancel accepts an illegal state. Scenario tests chain real calls, pass data between steps, and hand the agent evidence to fix with.
Testing
The backend was three weeks late. We shipped the frontend anyway.
A concrete sprint diary: one OpenAPI file drove a local mock with latency and error overrides, a four-step checkout scenario with an HTML report, live docs, derived database tables and a hosted MCP endpoint while the real API did not exist yet.