Jev Engineering: what a decision layer changes about the agent loop, and what it doesn't
Jev Engineering is usually compressed into one line — an LLM writes, Jev decides, code acts — but the term covers two different things: a routing pattern that is cheap to adopt, and a falsifiable architectural argument from TypeSafe's founder about how per-turn context, routing, tools and permissions should be decided. This piece walks the substrate (state plus typed questions, Choice/Score/Noul, parallel sampling, $0.042 per million input tokens), the routing arithmetic that shows naive model routing can cost more than staying on the expensive model, the fan-out pattern that actually holds up, the jagged edges in jev-1.13, and the gap between the self-run headline numbers and what third parties report.
