Harness

@nylorun/harness/run · beta

Advanced: in-process engine

import { run, bindingFromAgent } from "@nylorun/harness/run";

const result = await run({
  binding: bindingFromAgent(agent.build()),
  input,
  state,
  onModelCall: adapter,
  info,
  signal,
  onEvent,
  record,
});

run() is the public engine surface. It returns Promise<RunResult>. Application definitions have no .run(). The /engine specifier and hosted-execution names are gone; use /run and the durable names below.

This page is advanced host guidance. The taught application path is sessions plus a connected executor.

`BoundRunOptions` and `RunBinding`

Access: @nylorun/harness/run → run, RunBinding, BoundRunOptions, bindingFromAgent

Name	Type	Required	Description
`binding`	`RunBinding<Info>`	Yes	Manifest plus local implementations.
`input`	`ExecutionInput`	Yes	User message or a pause continuation.
`onModelCall`	`ModelAdapter`	Yes	Model adapter for this invocation.
`state`	`ExecutionState`	No	Prior returned state. Omit to start empty.
`info`	`Info`	No	Host identity for hooks and tools.
`signal`	`AbortSignal`	No	Cooperative cancellation. Abort settles as `cancelled`.
`onEvent`	`(event: ExecutionEvent) => void \| Promise<void>`	No	Live observations (not Runtime SSE).
`record`	`(state: ExecutionState) => void \| Promise<void>`	No	Awaited persistence barrier.

bindingFromAgent(agent) builds a RunBinding from an authored BuiltAgent. Bindings contain local functions and are not a wire format.

Statuses: completed | paused | cancelled | failed. Each returns serializable state.

Durable execution

Access: @nylorun/harness/run → runDurable, createDurableCheckpoint, DurableHost, DurableCheckpoint, DurableResult

Rename map (no aliases): runHosted → runDurable, createHostedCheckpoint → createDurableCheckpoint, EngineHost → DurableHost, EngineBinding → RunBinding.

Durable execution reconstructs progress from a checkpoint and individually journaled effect outcomes. Engine version is hosted-2. Checkpoint version is 1. Protocol version is 1. Manifest schema is 4.

A hook effect runs one hook point for every capability that registered it. Effect ids use stable names (before-turn, before-step:<stepId>, after-step:<stepId>, after-turn:<stepId>).

Model adapters

Custom hosts supply onModelCall. Translators for provider wire formats live on @nylorun/harness for host authors. Application users configure the provider in the Runtime vault, not on the agent.

Guide: HOST_CONTRACT.md.