Link to the code that reproduces this issue

https://github.com/Lebuin/repro-nextjs-duplicate-cookies

To Reproduce

1. Start the application in development mode
2. In a terminal, run curl -H "Cookie: sessionid=a; sessionid=b" http://localhost:3000

Current vs. Expected behavior

According to the docs:

Getting all cookies

You can use the (await cookies()).getAll() method to get all cookies with a matching name. If name is unspecified, it returns all the available cookies.

In my reproduction, I'm passing 2 cookies with the same name "sessionid". I expect getAll() to return an array containing both values. Instead, it only returns the last encountered value.

• Expected: {"Cookie header":"sessionid=a; sessionid=b","All cookies":["sessionid=a", "sessionid=b"],"Matching cookies":["sessionid=a", "sessionid=b"]}
• Actual: {"Cookie header":"sessionid=a; sessionid=b","All cookies":["sessionid=b"],"Matching cookies":["sessionid=b"]}

The fact that the method getAll(name) exists at all, makes me think that my expectations do match to way the cookie store was designed.

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #124-Ubuntu SMP PREEMPT_DYNAMIC Tue May 26 13:00:45 UTC 2026
  Available memory (MB): 15887
  Available CPU cores: 8
Binaries:
  Node: 24.14.1
  npm: 11.11.0
  Yarn: N/A
  pnpm: 10.14.0
Relevant Packages:
  next: 16.3.0-canary.70 // Latest available version is detected (16.3.0-canary.70).
  eslint-config-next: N/A
  react: 19.2.7
  react-dom: 19.2.7
  typescript: 5.9.3
Next.js Config:
  output: N/A

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

Cookies

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

next dev (local), next start (local)

Additional context

No response