Video Archive Search & Q&A Engine Build Blueprint

One-page reference for assembling a video archive search-and-Q&A engine with multimodal RAG: the index-once / cite-always two-rule spine, the two-half reference architecture, the build-vs-buy verdict per component, the 2026 embedding-and-answer model field with the Marengo 2.7 sunset, the two-line cost model (one-time index vs per-question) against the long-context baseline, the five-milestone build order, and the three governance gates (permissions, privacy of people in the footage, audit).