Renaming the distDir and using "output: export" seems to render "npm run start" unusable

Link to the code that reproduces this issue

https://codesandbox.io/p/devbox/npm-run-start-broken-t9z2fd

To Reproduce

1. I start clean by deleting both the .next and build folders if present.
2. Run the "build" task; this runs npm run build which runs next build
3. .next and build folders are created successfully. Run the "prod" task; this runs npm run start which runs next start
4. Error propagates

Current vs. Expected behavior

I am trying to test my production build locally. We are using static exports for our application and we have renamed the typical "out" folder to "build" in next.config.mjs. Everything builds successfully (and I have deployed it on production just fine), but running npm run start (which is really next start) cannot seem to find the production build.

I get this error:

Error: Could not find a production build in the 'build' directory. 
Try building your app with 'next build' before starting the production server.
https://nextjs.org/docs/messages/production-start-no-build-id

This is my next.config.mjs file:

/** @type {import('next').NextConfig} */
const nextConfig = {
    output: 'export',
    distDir: 'build',
    reactStrictMode: false,
    images: {
        unoptimized: true,
    },
}

export default nextConfig

The .next folder seems to contain the BUILD_ID but the build folder, which contains all the static exports, does not have a BUILD_ID and I think that is what npm run start is looking for based on the URL the error message points to. Any suggestions on how to run the production build with npm run start?

I understand my environment info below dictates things are out of date, but my codesandbox above should be using the latest NextJS and it still doesn't work there.

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP PREEMPT_DYNAMIC Thu Nov 7 15:41:49 EST 2024
  Available memory (MB): 15736
  Available CPU cores: 4
Binaries:
  Node: 20.5.1
  npm: 9.8.1
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 14.2.16 // An outdated version detected (latest is 15.0.3), upgrade is highly recommended!
  eslint-config-next: 14.2.16
  react: 18.3.1
  react-dom: 18.3.1
  typescript: 5.5.3
Next.js Config:
  output: export
 ⚠ An outdated version detected (latest is 15.0.3), upgrade is highly recommended!

Which area(s) are affected? (Select all that apply)

Developer Experience

Which stage(s) are affected? (Select all that apply)

next start (local)

Additional context

No response

Start with the linked CodeSandbox and its next.config.mjs, then run the reported npm run build and npm run start commands after removing .next and build. Inspect how output: export and distDir: 'build' affect the generated directories and production-start lookup. Done means the reported local production workflow has a documented or verified outcome.