# Workflow SDK adds idempotent starts

Source: [Vercel](https://vercel.com/changelog/atomic-start-hooks-in-the-workflow-sdk)  
Feed7 permalink: https://feed7.dev/p/atomic-start-hooks-in-the-workflow-sdk-1jf1nj8  
Published: 2026-11-04T18:55:00.000Z  
Trust: Official Source (official_source)

## Why Included

Workflow SDK 5.4.0 atomically admits a run and claims its hook, preventing duplicate starts from racing through a separate lookup and start.

## Source Summary

In **Workflow SDK 5.4.0**, `start()` can admit a run and claim a hook atomically. A duplicate token raises `HookConflictError` and identifies the run that owns it.

## Practical Implication

Use a domain identifier such as an order or request ID as the token to make starts idempotent. For duplicates, `resumeHook` can route the payload to the existing run; early payloads are buffered and delivered in order.

## Agent-Ready Context

In **Workflow SDK 5.4.0**, `start()` can admit a run and claim a hook atomically. A duplicate token raises `HookConflictError` and identifies the run that owns it.

Use a domain identifier such as an order or request ID as the token to make starts idempotent. For duplicates, `resumeHook` can route the payload to the existing run; early payloads are buffered and delivered in order.

`experimental_minRetention` keeps a token unavailable after the run ends. The material does not specify when that option becomes stable.

## Connected Context

Feed7 judgment across 1009 accumulated Signals:

This makes workflow start idempotency concrete: a domain token can atomically identify an existing run and hook, with duplicate payloads routed to that run and buffered in order. It narrows the general need for idempotency and recovery to a specific SDK mechanism; retention beyond run completion remains experimental.

- [AI Agents Are Just Distributed Systems Now — Salman Munaf, TikTok](https://feed7.dev/p/ai-agents-are-just-distributed-systems-now-salman-munaf-tiktok-1v4yc47) — The talk identifies idempotency and explicit recovery as distributed-systems requirements when tool outcomes are uncertain; this SDK feature supplies a concrete mechanism for deduplicating workflow starts and routing duplicate payloads.
- [Pause workflows for approval with Chat SDK](https://feed7.dev/p/chat-sdk-durable-approvals-1yfmvu0) — Both describe durable workflow handling across asynchronous events: Chat SDK suspends for a human decision, while Workflow SDK buffers early hook payloads and resumes the owning run.

## Context Map

- Layer: infra
- Domains: coding
- Topics: agent-reliability, tool-use

## Uncertainty

- `experimental_minRetention` keeps a token unavailable after the run ends. The material does not specify when that option becomes stable.

## Agent Instruction

Use this item as source-backed context. Do not invent claims beyond the linked source. If this item conflicts with another source, call out the conflict.