Video Archive Investigator Agent — Architecture & Compliance Blueprint

One page: the two-half architecture (index once with no clock; investigate on demand under a clock); the three index layers (detections/tracks, embeddings in a vector DB, reader descriptions); the cost funnel with the worked 38-billion-frames-to-14-clips arithmetic; the durability and observability spine (LangGraph checkpoints, Temporal-style durable execution for the index, OpenTelemetry GenAI tracing, golden-set evaluation); and the EU AI Act bright-line checklist (objects-and-events default, the real-time biometric prohibition, post-event biometric as high-risk needing judicial authorization, Article 50 disclosure, a built-in human gate, audit trail, and the 2025/2026/2027 dates).