Pages router: `meta` element doesn't update on navigation

[eostrom-livefront]

Link to the code that reproduces this issue

https://codesandbox.io/p/devbox/sad-pike-2zgvvw

To Reproduce

1. Start the application in development (next dev)
2. Go to the home page.
3. Inspect the page in devtools.
4. Note that the head for the iframe contains <meta name="description" content="Home metadata">, as declared in the Home component.
5. Click the link.
6. Inspect the page in devtools.
7. Note that the head for the iframe still contains <meta name="description" content="Home metadata">, even though the Destination component declares it with different content (and the same key).
8. Reload the iframe.
9. Inspect the page in devtools.
10. Note that the head for the iframe contains <meta name="description" content="Destination metadata">, as declared in the Destination component.

Current vs. Expected behavior

The meta tag should have the content declared in the current page component.

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP PREEMPT_DYNAMIC Sun Aug  6 20:05:33 UTC 2023
  Available memory (MB): 4102
  Available CPU cores: 2
Binaries:
  Node: 20.9.0
  npm: 9.8.1
  Yarn: 1.22.19
  pnpm: 8.10.2
Relevant Packages:
  next: 15.4.2-canary.0 // Latest available version is detected (15.4.2-canary.0).
  eslint-config-next: N/A
  react: 19.0.0
  react-dom: 19.0.0
  typescript: 5.1.3
Next.js Config:
  output: N/A
Done in 2.06s.

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

Metadata

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

next dev (local)

Additional context

Also observed on Next 15.4.1.

I can't find documentation that says meta tags should be updated on navigation, but it worked under Next 15.2.3. The docs say that the "contents of head get cleared upon unmounting the component," but that doesn't seem to be happening.

[eostrom-livefront]

Also NOT observed on Next 15.3.1-canary.12. (I was hoping the "head" mention in the release notes was related.)

I.e., it broke somewhere between 15.3.1-canary.12 and 15.4.1.

[github-actions]

This closed issue has been automatically locked because it had no new activity for 2 weeks. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.