The `.next/standalone/` output folder doesn't contain any sourcemaps

Link to the code that reproduces this issue

https://github.com/afgomez/test-next

To Reproduce

Not all sourcemaps are copied over when building a standalone build.

~/code/test-next[main]% pnpm run build
~/code/test-next[main]% find .next/standalone/.next/server/chunks -name '*.js.map' | wc -l
       0
~/code/test-next[main]% find .next/server/chunks -name '*.js.map' | wc -l
      27

However, the copied files do reference a sourcemap

~/code/test-next[main]% grep -r sourceMappingURL .next/standalone/.next/server/chunks | wc -l
      27

Current vs. Expected behavior

Expected:

• All sourcemaps are copied into the standalone/ folder.

Actual:

• No sourcemaps are copied into the standalone/ folder.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.2.0: Tue Nov 18 21:09:56 PST 2025; root:xnu-12377.61.12~1/RELEASE_ARM64_T6041
  Available memory (MB): 49152
  Available CPU cores: 14
Binaries:
  Node: 25.6.1
  npm: 11.9.0
  Yarn: 1.22.22
  pnpm: 10.29.3
Relevant Packages:
  next: 16.2.0-canary.37 // Latest available version is detected (16.2.0-canary.37).
  eslint-config-next: N/A
  react: 19.2.4
  react-dom: 19.2.4
  typescript: 5.9.3
Next.js Config:
  output: standalone

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

Output

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

next build (local)

Additional context

I can also reproduce this issue in Next 16.1.5.

I could not find anything in the docs mentioning that this is expected behaviour, or that it is configurable in any way.

I noticed because we run the app with node --enable-source-maps, but the stack traces still contained references to minified files. A fix for this issue will make my debugging sessions much easier 🙇

Reproduce the issue in the linked test-next repository with pnpm run build and output: standalone. Compare sourcemaps and sourceMappingURL references under .next/server/chunks and .next/standalone/.next/server/chunks; done means the standalone output contains the referenced sourcemaps and node --enable-source-maps produces useful stack traces.