Engineers who sit on your floor and build from day one, from a plain-language primer to contract design. Covers why FDEs move problems forward (5 reasons), how they differ from contract development (comparison), a fill-in checklist of 19 pitfalls for running it in-house, 8 questions to vet a vendor, and 10 pieces of advice. Based on primary and near-primary sources including MIT NANDA, a16z, OpenAI, AWS, and SEC filings.