single-dev-server git:20260828.d3bb9bcA

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---
description: Never start a second localhost Next.js server. Use the existing one.
alwaysApply: true
---

# One localhost only

Never start a second `bun run dev`, `next dev`, or `next start`.

Two Next.js processes share `.next`. That corrupts the Turbopack cache (missing `.sst` files, `/_app` panics, 500s on automation ticks).

## Before you start anything

1. Check Cursor terminals and listeners on 3000, 3001, and 3002.
2. If a Next.js server is already running, use that URL. Do not spawn another.
3. If 3000 is taken, Next will silently bind 3001 or 3002. That is a second server. Do not do that.

## If the existing server is dead or the cache is corrupt

1. Stop every `next` / `next-server` process first.
2. Only then `rm -rf .next` if you saw SST or Turbopack cache errors.
3. Start exactly one `bun run dev`.

Verify against the existing server (`http://localhost:3000` unless its own logs say otherwise).