You send a sample of real outputs and a description of the workflow. No account access, no credentials, no integration. I work through a 16-point failure taxonomy covering model errors (schema drift, invented identifiers, stale retrieval, silent truncation), plumbing (duplicate execution on retries, partial multi-step writes, empty results read as "nothing to do", unbounded loops), drift (model version changes, locale and encoding, time zones), and the failures with a customer on the other end (instructions arriving inside ingested data, commitments made on your behalf, personal data reaching somewhere new).