Diagnose staged OCR failures at the provider boundary

Diagnose staged OCR failures per stage and provider rather than from a generic OCR is down symptom. Define the request population, classify failures by stage, model, and provider response, and compare adjacent stages over the same time window. A healthy upstream text-recognition stage alongside failures in structured extraction narrows the investigation to the downstream boundary and can justify a scoped fallback test.

This method does not prove that a replacement model is schema-compatible, accurate, credentialed, or available at the required capacity. Historical success on a narrower contract is availability evidence for that contract, not equivalence evidence for the current route. Validate fallback outputs against the exact schema and field-level quality requirements before routing traffic.