fix(router-core): handle constructor search fields without throwing

[Tnalxmsk]

🎯 Changes

Visiting /?constructor=null with the default search parser throws during client router initialization, before validateSearch can run, even with search.strict: true. Client navigation with the same search value also throws. A JSON constructor object whose prototype.hasOwnProperty is not callable triggers a similar failure.

isPlainObject reads the input's constructor field as constructor metadata. Guard the nullable prototype access and use the existing hasOwn helper instead of calling a method on that metadata.

Add regression coverage for initial loading with strict search validation and for preserving constructor search values during client navigation. The failing inputs were reproduced with @tanstack/react-router@1.170.35 in a production browser bundle; with the fix, the route renders and subsequent navigation works.

Validation

• Before the fix, three of the five new regression cases fail; all five pass with the fix.
• Router Core unit tests, all six configured TypeScript checks, lint, and build pass locally. The production browser reproduction also initializes and navigates successfully after the fix.

✅ Checklist

• I have followed the steps in the Contributing guide.
• I have tested code changes locally with the relevant test commands, or tests do not apply to this pull request.
• I fully understand the code in this pull request, including any code generated with AI assistance.

🚀 Release Impact

• This change affects published code, and I have generated a changeset.
• This change is docs/CI/dev-only (no release).

Summary by CodeRabbit

• Bug Fixes
  • Fixed router initialization and navigation crashes when search parameters include a constructor field.
  • Search parameters with null, numeric, text, or object values are now safely encoded, parsed, and preserved in the URL and router state.
  • Improved handling of search parameter objects with missing constructors or custom hasOwnProperty values.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Advanced

Run ID: 1bbff3ae-bec8-44bd-9a80-afec2ab0920f

📥 Commits

Reviewing files that changed from the base of the PR and between 6494e75 and 47f1db3.

📒 Files selected for processing (3)

• .changeset/green-areas-shine.md
• packages/router-core/src/utils.ts
• packages/router-core/tests/search-constructor.test.ts

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

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📝 Walkthrough

Walkthrough

The router now safely processes search parameters with a constructor key. The plain-object check handles null constructors and objects that shadow hasOwnProperty. Tests cover initial URL parsing and client navigation.

Changes

Constructor search parameter handling

Layer / File(s)	Summary
Safe plain-object checks and router coverage packages/router-core/src/utils.ts, packages/router-core/tests/search-constructor.test.ts, .changeset/green-areas-shine.md	isPlainObject guards missing constructors and uses the shared hasOwn helper. Tests cover constructor values during initialization and navigation. A patch changeset records the fix.

Priority: ➖ Normal

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

Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 47f1d

Constructor-valued search parameters are handled safely during router initialization and client navigation, with the reported crash paths covered by tests.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the router-core fix for failures caused by constructor search fields.
Description check	✅ Passed	The description explains the failure, implementation, regression tests, validation results, checklist completion, and changeset release impact.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files. (1 skipped: 1 …
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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