fix(router-core): preserve encoded slashes in splat params

[xianjianlf2]

Fixes #7871.

Splat params span multiple path segments, so decoding the whole splat with decodeURIComponent makes an encoded slash inside a segment indistinguishable from a real path separator.

This decodes splat params segment-by-segment and keeps %2F encoded inside each segment. Other encoded characters in the segment, like %20, %23, and %3D, are still decoded as before. The same helper is used for fuzzy ** params.

Tests:

• pnpm --dir packages/router-core test:unit --run tests/path.test.ts
• pnpm --dir packages/router-core test:eslint
• pnpm --dir packages/history build && pnpm --dir packages/router-core test:types:ts70

Summary by CodeRabbit

• Bug Fixes
  • Fixed wildcard route parameters so encoded slashes remain part of a single path segment instead of being treated as separators.
  • Improved decoding of reserved characters in wildcard and fuzzy catch-all route matches.
  • Preserved the distinction between encoded slashes and actual path separators.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: eb0e52a6-0f51-4c99-a2fe-a57984b4d09e

📥 Commits

Reviewing files that changed from the base of the PR and between 88f366a and cb9af0b.

📒 Files selected for processing (2)

• packages/router-core/src/new-process-route-tree.ts
• packages/router-core/tests/path.test.ts

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📝 Walkthrough

Walkthrough

Splat parameter decoding now preserves encoded slashes within segments while decoding other characters. Wildcard and fuzzy catch-all extraction use the new behavior, with tests covering both matching modes.

Changes

Splat parameter decoding

Layer / File(s)	Summary
Segment-preserving splat decoding packages/router-core/src/new-process-route-tree.ts	Adds segment-wise splat decoding and applies it to wildcard (*) and fuzzy catch-all (**) parameters.
Splat decoding coverage packages/router-core/tests/path.test.ts	Tests encoded slashes, real separators, reserved characters, and fuzzy catch-all decoding.

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

Suggested labels: package: router-core

Suggested reviewers: sheraff

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	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: preserving encoded slashes in router-core splat params.
Linked Issues check	✅ Passed	The changes satisfy #7871 by preserving encoded slashes in splat and fuzzy params while keeping other decoding behavior intact.
Out of Scope Changes check	✅ Passed	The code and tests stay focused on splat-param decoding and do not introduce unrelated changes.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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