Build Agents with the SDK

Navigate the SDK contracts used to author Agent behavior, durable execution, Tools, Resources, and analytics.

Use @constal/sdk inside the immutable Agent package. The smallest useful Agent reads accepted history, makes one model turn, and returns a result that the runtime records durably:

Minimal Agent

import { agent, type HistoryView } from "@constal/sdk";

export default agent({
  id: "support", version: "1.0.0", model: "model",
  async onMessage(message, ctx) {
    const history = await ctx.ledger.view<HistoryView>("history");
    const turn = await ctx.turn({
      system: "Resolve the request accurately.",
      objective: message,
      context: { priorFacts: history.facts },
    });
    return { answer: turn.message.content };
  },
});

model is a logical Resource binding, not caller-selected provider input. ctx.resources contains only accepted CRNs, and Credential bytes never enter Agent code.

Add a durable boundary

async onMessage(message, ctx) {
  if (message.kind === "checkpoint") {
    return ctx.commit({ kind: "checkpoint", payload: message.payload });
  }
  return { accepted: true };
}

Use Durable Agent patterns for waits and subtasks, Resources SDK guide for effects, and Analytics SDK guide for typed events. Deployment remains a Console, CLI, or Platform API operation; it is intentionally absent from Ctx.