Vercel introduces open-source tool for reliable coding agents

Vercel has launched durable-harness, an open-source package designed to ensure coding agent sessions remain uninterrupted despite crashes and timeouts. The tool wraps existing harnesses like Pi, OpenCode, Claude Code, and Codex without altering their core functionality. Each session is stored in a durable log, ensuring that no work is lost even if a function fails. This addresses a key challenge for teams migrating coding agents from local environments to the cloud, where persistent storage and session tracking are often lacking. By leveraging Vercel’s Workflow SDK, durable-harness stores session data in a World, which integrates storage, a queue, and a stream into a single interface. This allows for seamless recovery of sessions, as each step of a turn is recorded in a durable log and can be resumed from a queue if a function fails. The system also mirrors session files into the log, preserving transcripts, rollouts, and event stores from various harnesses. Model-chosen commands are stored in the log, with a limit of 64 KB per entry. Vercel highlights that the agent code remains consistent across different environments, with just two environment variables needed to switch to Postgres.