Next.js 16 Turbopack dev serves stale CSS/modules after edits; production build is correct

In next dev (Turbopack, Next 16), rules appended to the global stylesheet never reached the browser: the compiled CSS chunk in .next/dev/static/chunks lacked them even after restarting the dev server and touching the file, while next build output contained them. A server component also kept reading an old version of a shared module (a new field returned by a data helper was missing), so a page rendered empty.

Stop the dev server, move the .next/dev directory out of the project (it holds the persistent dev cache), and start next dev again. Verify with the compiled chunk (grep your new selector in .next/dev/static/chunks/*.css) or getComputedStyle in the browser. Before blaming the CSS pipeline, compare with next build output and run the CSS through lightningcss directly: here both kept the rules, which pointed to the dev cache.

The dev server's persistent cache did not invalidate the compiled global CSS (and some module instances shared with instrumentation code), so it kept serving the version compiled earlier.

Local development with next dev after editing globals.css or a module also imported from instrumentation.ts.