Steps

step() records local non-determinism once so it replays identically on resume. Use it for anything that decides which effects run next but isn’t a tool or LLM call, like the current time, a random choice, or a fresh id.

import { step } from "rebuno";

const now = await step("now", () => Date.now());
const chosen = await step("pick_winner", ({ candidates }) => candidates[0], { candidates });

On resume the handler re-runs from the top. Calling Date.now() or Math.random() directly gives a different value the second time, so the effects that follow carry different arguments. Different arguments mean different step ids, and the kernel runs those effects again for real instead of replaying them. See determinism and step ids.

Signature

function step<T>(
  name: string,
  fn: (args: Record<string, unknown>) => T | Promise<T>,
  args?: Record<string, unknown>,                   // default {}
  idempotency?: "safe_to_retry" | "at_most_once",   // default "safe_to_retry"
): Promise<T>

name is the step’s target, the same field a policy rule matches on. The step id itself is derived by the kernel.
fn is the work to run. It’s called as fn(args), with the whole args object as the single argument.
args is the payload used for step identity, and is passed to fn. Omit it (default {}) when fn takes no arguments.
idempotency mirrors defineTool: safe_to_retry (default) for reads and non-determinism, at_most_once for local side effects that must not re-run on resume.

The result has to be JSON-serializable, since it’s recorded.

What it records

A step() call is recorded with kind local and travels the same submission path as a tool call. Replay, policy, and idempotency all work the same way. Policy treats local as a separate kind. A local step that matches no rule is allowed whatever default_action says, so a deny-by-default bundle won’t block one. Calling step() outside an active execution throws an Error.

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Reference

Signature

What it records

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​What it records

Signature

What it records