Turbopack: HMR stops updating after client navigation

Link to the code that reproduces this issue

https://github.com/g-wn/next-hmr-repro/

To Reproduce

1. Clone the repro, install dependencies, and start dev server
2. Open http://127.0.0.1:3000
3. Click Page B
4. Edit the heading in app/b/label.js and save. Note it stays unchanged in the browser.
5. Reload the page. Note the edit appears.
6. Edit again. Note the browser now updates w/out reloading - as expected.

Current vs. Expected behavior

Following the steps from the previous section, I expect that editing a file after client navigation will be reflected w/out a manual page reload. Currently, a manual reload is required after client navigation.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 27.0.0: Tue Aug 11 21:05:48 PDT 2026; root:xnu-13432.1.9~1/RELEASE_ARM64_T6041
  Available memory (MB): 65536
  Available CPU cores: 16
Binaries:
  Node: 24.14.1
  npm: 11.13.0
  Yarn: N/A
  pnpm: 10.8.1
Relevant Packages:
  next: 16.4.0-canary.31 // Latest available version is detected (16.4.0-canary.31).
  eslint-config-next: N/A
  react: 19.2.6
  react-dom: 19.2.6
  typescript: N/A
Next.js Config:
  output: N/A

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

Linking and Navigating, Turbopack

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

next dev (local)

Additional context

Issue was reproduced w/

• Next.js 16.3.5 and 16.4.0-canary.31
• React 19.2.6 and Node 24.14.1
• Arc and Chrome browsers
• MacOS

For comparison, the behavior works as expected using --webpack

🤖 Initial AI investigation suggests that Turbopack's page-specific HMR subscription is registered on a full page load but not after client-side nav. In browser testing, loading the missing registration script manually restored hot updated w/out reloading the page. This points to a missing subscription rather than a file-watching or browser caching issue.

Start with the linked reproduction and follow the steps using next dev, then compare the behavior with --webpack. Focus on the Turbopack HMR behavior after navigating to Page B and editing app/b/label.js, including the missing subscription suggested in the report. Done means edits update without a manual reload after client navigation.