nextjs - 💡(How to fix) Fix App Router: root generateMetadata reruns a shared fetch on sibling navigation even when the shared layout UI is preserved [1 comments, 2 participants]

Link to the code that reproduces this issue

https://github.com/Innei/nextjs-generate-metadata-shared-fetch-repro

To Reproduce

1. Clone the reproduction repo.
2. Run npm install.
3. Run npm run build.
4. Run npm run start.
5. Open http://localhost:3000/alpha.
6. Check the server logs and note the latest [shared-layout] fetch.
7. Navigate to /beta using the in-app link.
8. Check the server logs again.

Current vs. Expected behavior

Current behavior:

• The shared layout UI is preserved across sibling navigation.
• The root generateMetadata() still re-evaluates on navigation.
• Because generateMetadata() calls the same shared fetch as the preserved layout, the shared fetch runs again and logs a new [shared-layout] fetch.
• The client navigation request is an _rsc request and includes a refetch marker in next-router-state-tree.

Expected behavior:

• If a shared layout segment is preserved across sibling navigation, root metadata that only depends on that preserved segment could be reused instead of triggering the shared fetch again.
• If that reuse is intentionally not possible, the docs should state more explicitly that preserved layouts do not imply preserved metadata evaluation or preserved shared data reads.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.6.0: Wed Nov  5 21:33:59 PST 2025; root:xnu-11417.140.69.705.2~1/RELEASE_ARM64_T8112
  Available memory (MB): 24576
  Available CPU cores: 8
Binaries:
  Node: 22.21.0
  npm: 11.6.2
  Yarn: N/A
  pnpm: 10.26.2
Relevant Packages:
  next: 16.2.0-canary.99
  eslint-config-next: N/A
  react: 19.2.4
  react-dom: 19.2.4
  typescript: N/A
Next.js Config:
  output: N/A

Which area(s) are affected?

• Linking and Navigating
• Metadata

Which stage(s) are affected?

• next dev (local)
• next start (local)

Additional context

• The repro intentionally uses headers() to keep the route dynamic.
• getSharedLayoutData() is wrapped with react cache().
• This shows that the repeated shared fetch is not a duplicate call within a single render pass; it happens across client navigations.
• The repro is intended to be tested against next@canary, per the official bug report template guidance.
• I searched the current issue list and did not find an exact duplicate for "root generateMetadata() reruns a preserved shared fetch on sibling route navigation"; the closest related item I saw was #62162, which is about clarifying React.cache() usage in generateMetadata().
• If this is considered expected behavior, this report can be treated as an optimization or documentation request rather than a correctness bug.