durable-harness runs coding-agent harnesses (Pi, OpenCode, libfx's fx,
Claude Code and Codex) as durable agents on a
Workflow SDK World. Each session is a workflow
run: its conversation, the turn in flight and every model and tool call are
in the run's event log, so a crash anywhere resumes the turn from the log on
another machine, and a tool call that isn't safe to repeat is never run twice.

[!NOTE]
durable-harness is experimental: it's on 0.0.x, and its API may change
between releases.

Quick start

Install it with a harness, here Pi with
pi-durable, in a
Next.js app:

npm install durable-harness @earendil-works/pi-durable @earendil-works/chord @earendil-works/pi-ai just-bash

Open Pi's own durable Harness on a World-backed storage. Agents are
tool-less by default; Pi's coding tools go on a virtual workspace, whose files
live in the session's log:

// lib/agent.ts
import { BACKGROUND_CONTEXT as ctx } from '@earendil-works/chord/context';
import { createRegistry, Harness, type Storage } from '@earendil-works/pi-durable';
import { CodingTools, GATEWAY_PROVIDER, gatewayModels, resumeWith, virtualEnv } from 'durable-harness/pi-durable';

const models = gatewayModels();
const registry = createRegistry();
registry.install(CodingTools);

export const agent = { model: { provider: GATEWAY_PROVIDER, modelId: 'anthropic/claude-sonnet-4.5' } };
export const open = resumeWith((storage: Storage) => Harness.open(storage, { models, registry, env: virtualEnv() }, ctx));

Serve it from a chat route, and configure the integration:

// app/api/chat/route.ts
import { chatRoute } from 'durable-harness/pi-durable';
import { agent, open } from '@/lib/agent';

export const { GET, POST } = chatRoute({ open, agent, authorize: async (request) => { /* your auth */ } });

// next.config.ts
import type { NextConfig } from 'next';
import { withDurableHarness } from 'durable-harness/next';

const nextConfig: NextConfig = {
  // your existing config
};

export default withDurableHarness(nextConfig);

Choose your harness and framework in the
agent harnesses docs.

Harnesses

• Pi: durable-harness/pi-durable
  (recommended: Pi's own durable Harness on a World), or durable-harness/pi.
• OpenCode:
  durable-harness/opencode.
• fx: durable-harness/fx,
  libfx's kernel tools for its own durable agents.
• Claude Code and
  Codex:
  durable-harness/claude-code and durable-harness/codex. They run only in
  the session's own Vercel Sandbox, never in a shared Function
  (why).

Model-chosen commands and files run on a virtual workspace (virtual()) or
in the session's own Vercel Sandbox (sandbox()), never on the machine that
drives the session. See tools
and security.

Run anywhere

Local development uses the Workflow SDK's local World with no configuration.
Deploy to Vercel for managed storage, queuing and scaling, with sessions in
Agent Runs. To
self-host, use the Postgres World or any other
World: see
self-hosting.

Contributing

Contributions are welcome. Use
issues to collaborate
with the team, and read
CONTRIBUTING.md
before opening a pull request.

Security

If you find a security vulnerability in durable-harness, disclose it responsibly instead of opening a public issue.

To participate in our Open Source Software Bug Bounty program, please email
[email protected].
We will add you to the program and provide further instructions for submitting
your report.