fix(data-loaders): do not crash on duplicated SSR navigations

[re-thc]

A duplicated navigation to a route with loader server: false crashes on SSR with TypeError instead of resolving the navigation failure.

This fixes the crash.

Summary by CodeRabbit

• Bug Fixes
  • Repeated navigation to a route with a client-only data loader is now handled correctly, including when the navigation is identified as a duplicate.

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🔨 Latest commit	10e004c
🔍 Latest deploy log	https://app.netlify.com/projects/vue-router/deploys/6ac7ce74d25c6d0008cc1bfc

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Repository: vuejs/router/.coderabbit.yaml
• Review profile: CHILL
• Plan: Advanced
• Run ID: 60a51ea2-6bb2-4862-b2c4-12205bf9831e

📥 Commits

Reviewing files that changed from the base of the PR and between 42462bd and 10e004c.

📒 Files selected for processing (2)

• packages/router/src/experimental/data-loaders/navigation-guard.spec.ts
• packages/router/src/experimental/data-loaders/navigation-guard.ts

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📝 Walkthrough

Walkthrough

The duplicated-navigation cleanup now checks for a loader entry before resetting pending state. A server-side regression test verifies the initial navigation and repeated-navigation failure for a loader configured with server: false.

Changes

Navigation guard cleanup

Layer / File(s)	Summary
Handle missing entries in duplicated-navigation cleanup packages/router/src/experimental/data-loaders/navigation-guard.ts, packages/router/src/experimental/data-loaders/navigation-guard.spec.ts	The cleanup calls resetPending() only when a loader entry exists. The test verifies that the first push to /fetch succeeds and the second produces a duplicated-navigation failure.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 10e00

Repeated SSR navigation to a route with a server:false loader now avoids the missing-entry crash. The inspected path has no pending state to clean up, and no actionable merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: preventing crashes during duplicated SSR navigations in data loaders.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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commit: 10e004c

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.26%. Comparing base (42462bd) to head (10e004c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2831   +/-   ##
=======================================
  Coverage   88.26%   88.26%           
=======================================
  Files          78       78           
  Lines        6305     6305           
  Branches     2048     2048           
=======================================
  Hits         5565     5565           
  Misses        651      651           
  Partials       89       89           

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[posva]

Even if the fix is one char, I'm afraid it could hide other bugs in the future.

Do you have any realistic reproduction of this bug?

[posva]

But why would this happen during SSR? There is only one navigation on the server