Link to the code that reproduces this issue

https://github.com/albert4719/turbopack-deadcode-repro

To Reproduce

1. npm install
2. npm run build
3. grep the compiled action chunk in .next/server/chunks/ssr — the code after the switch is gone

Current vs. Expected behavior

A server action with a switch (one empty case + break, and default returning the same value as another case) loses all code after the switch in next build. It returns undefined for the empty case. Works fine in next dev. Details +
de-minified output in the repo README.

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 10 Pro
  Available memory (MB): 65179
  Available CPU cores: 32
Binaries:
  Node: 26.2.0
  npm: 11.13.0
  Yarn: 1.22.22
  pnpm: N/A
Relevant Packages:
  next: 16.2.9 // Latest available version is detected (16.2.9).
  eslint-config-next: N/A
  react: 19.2.4
  react-dom: 19.2.4
  typescript: N/A
Next.js Config:
  output: N/A

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

Turbopack

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

Other (Deployed), next start (local)

Additional context

No response