# Making every harness durable

By Steven Van · 2026-10-19

Guides cover Pi, OpenCode, fx, eve, Claude Code and Codex, with the last two experimental and running in a Vercel Sandbox.

Vercel has published guides for running Pi, fx, OpenCode, eve, Claude Code and Codex durably, so a crash or function timeout resumes the agent's turn instead of losing its work. The release is a new package, durable-harness, which extends the durability already built into eve and fx to other harnesses. The details are in [Vercel's harness documentation](<https://vercel.com/docs/agent-harnesses/harnesses>) and a [release post](<https://vercel.com/blog/making-every-harness-durable>), and the feature runs on [Vercel](<https://creatorstoolbox.com/tools/vercel>).

## The problem it addresses

Harnesses are built as long-lived processes that keep the session in memory, and agent tasks often run for minutes or hours. Locally, the workspace and session history sit on the same disk, so resuming interrupted work takes a simple prompt. In the cloud, a VM with persistent storage can replicate that setup, but it does not record which model and tool calls completed, and it does not resume interrupted turns after a crash. A failed turn or network error therefore means lost work.

Vercel also notes that not every agent task needs a sandbox. Database queries and API calls can run securely in functions, which keeps the required credentials out of the sandbox.

## What durable-harness does

It uses the same machinery that powers Workflow SDK to survive crashes and function timeouts. Vercel lists four uses:

- Run any of the supported harnesses durably on Vercel

- Self-host a harness with your own Postgres instance

- Make a local harness workflow durable

- Build your own durable harness

## Supported harnesses

Each guide sets up the agent, a chat route, and the route that resumes a turn after a crash.

- **Pi**, **OpenCode** and **fx** run in your function, with files in a virtual workspace or a Sandbox. Pi and OpenCode use durable-harness packages, and fx uses libfx.

- **eve** runs as an eve app that is durable by default.

- **Claude Code** and **Codex** run in a Vercel Sandbox, and both are marked experimental.

The durable-harness guides share one setup, shown for Next.js and for other frameworks. Shared pages cover tools, files and documents, observability (each session appears in Vercel Agent Runs), security, and self-hosting sessions in another World, such as Postgres, on your own servers.

![Vercel](<https://www.google.com/s2/favicons?domain=vercel.com&sz=128>)

Vercel

The platform for frontend developers — deploy, preview, and scale web apps and AI agents with zero config.

[View Vercel →](<https://creatorstoolbox.com/tools/vercel>)

[Original source](<https://vercel.com/blog/making-every-harness-durable>)

[Read Making every harness durable on Creators Toolbox](<https://creatorstoolbox.com/blog/vercel-making-every-harness-durable>)

---
Canonical source: https://creatorstoolbox.com/blog/vercel-making-every-harness-durable