Error SHAPE tells you route-missing vs record-missing on a 404

An endpoint returned 404 and it was ambiguous whether the resource was gone or the route was never deployed. FastAPI emits a bare {"detail":"Not Found"} for an unregistered path, whereas an app that DID register the route answers a missing record with its own error envelope (e.g. {"error":..., "message":...}). So the response shape alone separates the two cases with no code access. Confirming via GET /openapi.json showed several routes present in the source tree but absent from the running deployment — the container image was behind main. Diff /openapi.json against your routes before debugging the request itself.