Turbopack dev on macOS hits Watchpack fs.watch EMFILE on ancestor directories and app subtrees

Link to the code that reproduces this issue

https://github.com/wzrdgang/next-turbopack-emfile-macos-repro

To Reproduce

1. On macOS, clone the repro repo above.
2. Run npm install
3. Run npm run dev:debug
4. Observe repeated Watchpack Error (watcher): Error: EMFILE: too many open files, watch
5. Observe the debug watcher targets printed by the fs.watch preload in scripts/watch-debug.cjs
6. Run npm run build in the same repo and note that the build succeeds

Current vs. Expected behavior

Current behavior:

• Turbopack dev starts, then immediately emits repeated Watchpack EMFILE errors
• The debug logger shows fs.watch EMFILE events for ancestor directories like:
  • /Users
  • /Users/<user>
  • /Users/<user>/Documents/...
  • the project root
  • multiple app/... subdirectories
• The same run also triggers false Found a change in next.config.js. Restarting the server to apply the changes...

Expected behavior:

• next dev with Turbopack should watch only the needed project paths without entering an EMFILE loop
• A high ulimit -n should not still result in repeated native watcher failures
• Turbopack should not restart because of false-positive config change detection during watcher failure

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.6.0: Mon Jan 19 22:01:41 PST 2026; root:xnu-11417.140.69.708.3~1/RELEASE_ARM64_T8132
  Available memory (MB): 24576
  Available CPU cores: 10
Binaries:
  Node: 25.9.0
  npm: 11.12.1
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 16.2.3
  eslint-config-next: N/A
  react: 18.3.1
  react-dom: 18.3.1
  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)

next dev (local)

Additional context

• The repro intentionally creates a moderately wide App Router tree under app/ because the larger real-world app showed the same failure pattern.
• The failure reproduced with both Node 25.9.0 and Node 24.14.0 in local investigation.
• The repro still succeeds with npm run build, so the problem appears isolated to Turbopack dev watchers.
• A validated watcher-target excerpt is included in VALIDATED_WATCH_LOG.txt in the repro repo.
• In the larger Munimetric app, the same logger also showed native watch attempts on /Users, /Users/samhowell, /Users/samhowell/Documents, /Users/samhowell/Documents/munimetric, /Users/samhowell/Documents/munimetric/frontend, /Users/samhowell/Documents/munimetric/frontend/app, and many frontend/app/... route directories.
• In the larger app, webpack + polling works around the issue, but that bypasses Turbopack instead of fixing it.
• A first submission attempt was auto-closed as #93174 because the reproduction link was not inside a bot-parseable issue-form field. This issue uses the same public repro with the required field structure.

Validated watcher-target excerpt:

[fs.watch EMFILE event] /private
[fs.watch EMFILE event] /private/tmp
[fs.watch EMFILE event] /private/tmp/next-turbopack-emfile-macos-repro
[fs.watch EMFILE event] /private/tmp/next-turbopack-emfile-macos-repro/app
[fs.watch EMFILE event] /private/tmp/next-turbopack-emfile-macos-repro/app/about
[fs.watch EMFILE event] /private/tmp/next-turbopack-emfile-macos-repro/app/api
[fs.watch EMFILE event] /private/tmp/next-turbopack-emfile-macos-repro/app/internal
[fs.watch EMFILE event] /private/tmp/next-turbopack-emfile-macos-repro/app/states
Watchpack Error (watcher): Error: EMFILE: too many open files, watch
⚠ Found a change in next.config.js. Restarting the server to apply the changes...

Clone the linked reproduction, run npm install and npm run dev:debug, and inspect the watcher targets from scripts/watch-debug.cjs alongside VALIDATED_WATCH_LOG.txt. Compare the dev watcher behavior with npm run build and trace the Turbopack dev watcher path responsible for the ancestor and app-subtree watches. Done means repeated EMFILE errors and false next.config.js restart detection no longer occur.