Server Actions that are hybrid types are compiled to `{}` causing `TypeError`

Link to the code that reproduces this issue

To Reproduce

Start the application with npm run dev.
Click on "Create user".
Witness the Error: operation(...) is not a function when clearly it should have been an async function.

[!NOTE] Please refer to README.md for more information about this error.

Current vs. Expected behavior

Expected behaviour is for createUser to actually be compiled as an async function with a hybrid type. Not an empty object {}.

This wasn't the case and everything was fine up till next@14.1.0. Since next@14.1.1, I get this error. In the reproduction CodeSandbox, try running npm i next@14.1.0; npm run dev to see the app working fine.

If you prefer to run it locally, you can clone the repository here: https://github.com/purfectliterature/typeerror-starter.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.0.0: Thu May 30 21:30:12 PDT 2024; root:xnu-11215.0.31.511.2~1/RELEASE_ARM64_T6000
  Available memory (MB): 65536
  Available CPU cores: 10
Binaries:
  Node: 20.14.0
  npm: 10.7.0
  Yarn: 1.22.19
  pnpm: N/A
Relevant Packages:
  next: 14.2.4 // Latest available version is detected (14.2.4).
  eslint-config-next: 14.2.4
  react: 18.3.1
  react-dom: 18.3.1
  typescript: 5.4.5
Next.js Config:
  output: N/A

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

Output (export/standalone), Runtime, SWC, Webpack

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

next dev (local), next start (local)

Additional context

It was fine up till next@14.1.0 and it breaks in next@14.1.1.

Potentially related to https://github.com/vercel/next.js/issues/62953 (?) [I posted there!] but that was closed and my use case is still erroring even in the latest release of Next.js at next@14.2.4.

Please refer to my README.md for more information about the error, how to reproduce, and some more context about my use case. It's not that long and very concise!

vercel / next.js