Vite 8 bundledDev + CSS + PostCSS crash repro

Minimal reproduction of a hard build-time crash in Vite's experimental full-bundle dev mode (experimental.bundledDev: true) when a project imports a .css file and uses PostCSS.

When the CSS module is loaded through Rolldown's lazy bundling (e.g. via a dynamic import), Rolldown wraps it in a JavaScript proxy that keeps the original id but appends a ?rolldown-lazy=1 query. Vite's vite:css plugin matches on the .css extension and does not exclude the ?rolldown-lazy query, so it runs PostCSS on the JS proxy module. PostCSS then tries to parse JavaScript as CSS and throws:

[plugin vite:css] /.../src/global.css?rolldown-lazy=1:15:41
CssSyntaxError: [postcss] /.../src/global.css?rolldown-lazy=1:15:42: Unclosed string
    ...
    at runPostCSS (.../vite/dist/node/chunks/node.js:21166:66)
    at async compilePostCSS (.../vite/dist/node/chunks/node.js:21150:6)

This is a hard build-time crash — the server starts but the bundle fails to build, and no page reload recovers it.

Reproduce

npm install
npm run dev
# open http://localhost:5173/ in a browser

The browser shows a "Bundling in progress" screen with an error overlay, and the dev server terminal prints the CssSyntaxError: Unclosed string build error above.

The exact captured error output is in error-8.0.16.log.

Regression range

Version	Result
8.0.0 / 8.0.8 / 8.0.12	✅ works
8.0.13	❌ first broken
8.0.14 / 8.0.16	❌ broken

Introduced by 8.0.13's "bundled-dev: add lazy bundling support" (vitejs/vite#21406).

To verify the regression yourself:

npm install [email protected] --save-exact --save-dev && npm run dev   # works
npm install [email protected] --save-exact --save-dev && npm run dev   # crashes

Why these specific files

• vite.config.js — enables experimental.bundledDev: true.
• postcss.config.js — registers autoprefixer so PostCSS actually runs (the crash is inside runPostCSS). The CSS uses user-select, which autoprefixer rewrites, proving PostCSS is meaningfully in the pipeline.
• src/main.js — dynamically imports the CSS (await import('./global.css')). A dynamic import is what forces Rolldown to lazy-bundle the CSS module and emit the ?rolldown-lazy=1 proxy that triggers the bug.
• src/global.css — perfectly valid CSS (the crash is not a CSS-authoring error).