jev-harness-router

# jev-harness-router

**One fast call decides how an agent turn should run — then runs it.**

Before a harness spends a second on the real work, it has to answer four questions about
the turn in front of it. This asks all four in a single [Jev](https://docs.typesafe.ai/)
call, in about 350 ms, behind a deadline it is not allowed to miss.

| decision | how it is asked |
| --- | --- |
| **model tier** | not asked — derived in code from how hard the turn is and how much it touches |
| **effort budget** | same, from the same `Score` |
| **tools** | one `Noul` per tool, plus the tail of a ranking `Choice` |
| **skill** | one `Choice` over the catalogue, gated by four request-shape `Noul`s |



```ts
import { createRouter, defineCatalog } from "jev-harness-router";

const catalog = defineCatalog({
  models: [                                // cheapest first — the order is the ladder
    { tier: "fast", id: "claude-haiku-4-5", label: "Haiku", use: "Lookups, one-file edits." },
    { tier: "deep", id: "claude-opus-5",             label: "Opus",  use: "Design, cross-cutting work." },
  ],
  tools: {
    Read: { description: "Open a file the user named.", risk: "read" },
    Bash: { description: "Run a shell command.",        risk: "execute" },
  },
  skills: {
    debug: { description: "Work backwards from an error to its root cause." },
  },
});

const router = createRouter({ catalog });
await router.prewarm();                    // once, at startup

const route = await router.route({ message: "arreglá el bug de auth en el login" });

route.tier;    // "fast" | "deep"          — your names, not ours
route.model;   // "claude-opus-5"
route.effort;  // "low" | "medium" | "high" | "xhigh"
route.tools;   // ("Read" | "Bash")[]
route.skill;   // "debug" | null
route.source;  // "jev