next build --webpack drops semicolon after CSS @layer statement

Link to the code that reproduces this issue

https://github.com/Poliklot/next-css-layer-statement-semicolon-repro

To Reproduce

git clone https://github.com/Poliklot/next-css-layer-statement-semicolon-repro.git
cd next-css-layer-statement-semicolon-repro
npm install
npm run build
npm run inspect-css

The reproduction is intentionally small. The important source file is src/styles/layers.scss:

@layer reset, tokens, base, components, utilities;

It is imported before other global SCSS files in src/app/layout.tsx.

Current vs. Expected behavior

Current behavior: next build --webpack removes the semicolon after the CSS cascade layer statement in the emitted production CSS.

The built CSS starts like this:

@layer reset, tokens, base, components, utilities
@layer reset{*,:after,:before{box-sizing:border-box}body{margin:0}a{color:inherit;text-decoration:none}}

The layer statement is missing its required ; before the following @layer reset { ... } block. In browsers this makes the output invalid around the layer statement boundary, and the following reset layer can be ignored. In a real app this caused production-only styling differences: anchors became underlined again and form controls fell back to default/content-box sizing, while development looked correct.

Expected behavior: the emitted CSS should preserve a valid boundary between the layer statement and the following layer block, for example:

@layer reset, tokens, base, components, utilities;@layer reset{*,:after,:before{box-sizing:border-box}}

or otherwise output a valid equivalent CSS representation.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.3.0: Wed Jan 28 20:54:46 PST 2026; root:xnu-12377.91.3~2/RELEASE_ARM64_T6000
  Available memory (MB): 16384
  Available CPU cores: 8
Binaries:
  Node: 20.19.0
  npm: 11.13.0
  Yarn: 1.22.22
  pnpm: 8.7.6
Relevant Packages:
  next: 16.3.0-canary.31 // Latest available version is detected (16.3.0-canary.31).
  eslint-config-next: N/A
  react: 19.2.6
  react-dom: 19.2.6
  typescript: 6.0.3
Next.js Config:
  output: export

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

CSS, Output, Webpack

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

next build (local), Other (Deployed)

Additional context

This reproduces with the latest canary available at the time of testing (next@16.3.0-canary.31) and with next build --webpack.

The issue was originally noticed in a statically exported app deployed to Apache, but the linked reproduction shows that the invalid CSS is already emitted by the local production build before deployment.

A workaround is to avoid the layer statement form and declare empty layer blocks instead:

@layer reset {}
@layer tokens {}
@layer base {}
@layer components {}
@layer utilities {}

That keeps the emitted CSS valid in the affected app.

I searched for related issues before opening this. Existing issues like #64921, #79531, and #68476 look related to CSS order / cascade layers / cssnano, but I could not find an issue for this exact missing semicolon after a standalone @layer statement in a webpack production build.

Start with the reproduction's src/styles/layers.scss and src/app/layout.tsx, then run npm install, npm run build, and npm run inspect-css to inspect the emitted CSS. Trace the next build --webpack production CSS path responsible for removing the separator, and verify that the standalone @layer statement remains valid before the following layer block.