The best build writeup on this list: a real production system serving 3,683 employees and 241 billion tokens a month. Three layers worth copying wholesale. Zero-trust access and a single gateway at the front; a knowledge layer of service catalogues, MCP servers and AGENTS.md files generated across 3,900 repos; an enforcement layer of review agents that cite organisational standards by rule ID. The lesson to steal: route everything through one proxy from day one, so permissions, models and tracking update centrally without touching a single client.