Designing a Reliable PDF Translation Job Pipeline in TypeScript

Uploading a PDF and calling a translation model looks like a two-step feature. In production, it is a job pipeline with untrusted input, two different extraction paths, several expensive stages, and an output that can be fluent while still being wrong. That distinction matters for a small SaaS team. The translation request may come from support, sales, or an internal operations task. Nobody wants to operate a document platform, but the workflow still needs to answer basic questions: Was the upload actually a PDF? Does the file contain selectable text or scanned page images? Can a retry create a second charge or a conflicting result? What happens when page 37 fails after the first 36 pages succeed? How do we know the translated PDF is not blank or visually broken? When are the source and result deleted? The translation model is one component. Reliability comes from the system around it. Define the Job Contract First I would not let a file reach an extractor until the API has established a narrow contract. For example, a translation request might include: type TranslationStyle = " general " | " technical " | " academic " ; interface CreateTranslationJob { uploadId : string ; sourceLanguage : string | " auto " ; targetLanguage : string ; style : TranslationStyle ; idempotencyKey : string ; containsRestrictedData : boolean ; } The request should be rejected when the source and target languages are identical, the upload is missing, the target language is unsupported, or policy says the document cannot leave an approved environment. File validation should also be explicit. Do not trust the filename or browser-supplied MIME type. Check at least: the actual byte size; the file signature; whether the parser can open the document; whether the PDF is encrypted; the page count; whether the job fits the account or product limit. A 20 MB limit is simple to explain in a user interface, but size alone is not a good predictor of work. A compressed 200-page text PDF can be smaller th