Building a Production RAG Pipeline That Actually Survives Monday Morning

I spent three months building a document extraction API. The first version worked great in demos. It also silently hallucinated invoice totals, crashed when Claude hit rate limits, and had no way to tell me extraction quality was degrading until a customer filed a support ticket. This is the story of three patterns that turned it into something I'd actually deploy: circuit breaker model fallback, a golden eval CI gate, and two-pass extraction with automatic correction. The problem: documents are messy Every company that processes documents at scale hits the same wall. PDFs arrive in different layouts. Scanned images have OCR artifacts. Emails have attachments nested inside attachments. Template-based extraction tools break the moment a vendor changes their invoice format. I needed an API that could accept any document, figure out what it was, and extract the right fields without being pre-configured for each layout. Architecture: three services, seven steps Client -> FastAPI REST API -