Verdict: In 2026, building a working AI agent is close to a solved problem. Durable state, sandboxed execution, and observability are now platform primitives, not quarter-long engineering projects. What still breaks agents in production is not the model and not the scaffolding. It is missing context: the decisions, discussions, and tribal knowledge that live outside the code and the ticket the agent was handed. The fix is a deliberate context layer, and this guide shows you how to build one. ...