Echo agent

Smallest meaningful drover program. Define, run, read.

The five-line agent. Demonstrates the schema-validated input + output flow without any tools or extras.

echo.ts

import { Type } from "@sinclair/typebox";
import { defineAgent } from "@drover/core";
import { runAgent } from "@drover/facade";

const spec = defineAgent({
  id: "echo",
  systemPrompt:
    "Reply with a JSON object matching the outputSchema. No prose.",
  inputSchema: Type.Object({ word: Type.String() }),
  outputSchema: Type.Object({
    upper: Type.String(),
    length: Type.Integer(),
  }),
  model: "cheap",
  tools: [],
  quota: { maxTurns: 2 },
});

const handle = runAgent(spec, { word: "drover" });
for await (const e of handle.events) {
  if (e.kind === "usage") console.log("tokens:", e.usage.inputTokens + "/" + e.usage.outputTokens);
}
const r = await handle.result;
console.log(r.output);  // { upper: "DROVER", length: 6 }

Run:

bash

export OPENROUTER_API_KEY=sk-or-v1-...
bun echo.ts

Behaviour:

defineAgent types the spec so r.output is inferred as { upper: string; length: number }.
Input is validated before the model call. Garbage input = immediate InputValidationError.
Output is decoded against outputSchema. Failures get retried with a corrective user message; budget = outputRetries (default 2).
Promise never rejects — r.error populates on the error path.

What this skips that real agents need:

Tools — see the multi-agent example or Writing an agent.
Storage / pause-resume — see Pause / resume.
Plugins — see Plugins.

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