fix(core): make isWithinRoot case-insensitive on Windows

[mydd7]

Summary

isWithinRoot() compared paths with case-sensitive === / startsWith. On Windows that rejects valid in-root paths when the drive letter or folder casing differs (c:\... vs C:\...), which breaks ACP/IDE FS routing and ignore-path normalization.

Reuse isSubpath(), which already does a case-insensitive check on Windows (and Darwin).

Details

isSubpath() already uses path.win32 and case-insensitive relative() on Windows. isWithinRoot() was a second containment helper that did not.

macOS /private alias handling is unchanged; it now also goes through isSubpath().

Related Issues

Fixes #29000

How to Validate

1. On Windows, call isWithinRoot('C:\\Users\\proj\\file.ts', 'c:\\Users\\proj') — should be true.
2. packages/core tests: isWithinRoot on Windows (drive-letter casing, path-component casing, different drive).
3. Existing isWithinRoot cases still pass on POSIX.

Pre-Merge Checklist

• Updated relevant documentation and README (if needed)
• Added/updated tests (if needed)
• Noted breaking changes (if any)
• Validated on required platforms/methods:
  • MacOS
    • npm run
    • npx
    • Docker
    • Podman
    • Seatbelt
  • Windows
    • npm run
    • npx
    • Docker
  • Linux
    • npm run
    • npx
    • Docker

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[github-actions]

📊 PR Size: size/S

• Lines changed: 48
• Additions: +25
• Deletions: -23
• Files changed: 2

[mydd7]

CLA check is red until the Google CLA is signed at https://cla.developers.google.com/

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves an issue where path validation in the core package was failing on Windows due to case-sensitive comparisons. By migrating the logic to use the established isSubpath utility, the implementation now correctly accounts for Windows' case-insensitive file system behavior, improving the reliability of IDE file system routing and path normalization.

Highlights

• Path comparison logic: Refactored the isWithinRoot function to utilize the existing isSubpath utility, ensuring consistent and robust cross-platform path handling.
• Windows compatibility: Enabled case-insensitive path comparisons on Windows to prevent false negatives caused by drive letter or folder casing discrepancies.
• Testing: Added comprehensive unit tests to verify that isWithinRoot correctly handles case-insensitive paths on Windows while maintaining existing behavior on other platforms.

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[mydd7]

I signed the CLA.

[gemini-code-assist]

Code Review

This pull request refactors the isWithinRoot utility in packages/core/src/utils/fileUtils.ts to use the isSubpath helper, simplifying the path comparison and macOS symlink handling. It also introduces Windows-specific unit tests. The feedback points out that mocking process.platform inside a block already skipped on non-Windows platforms is redundant and that stubbing the global process object is risky and should be removed.

[gemini-code-assist]

Since this describe block is already skipped on non-Windows platforms using describe.skipIf(process.platform !== 'win32'), the tests inside will only ever execute on Windows. Consequently, mocking process.platform to 'win32' is completely redundant.

Furthermore, stubbing the global process object using Object.create(process, ...) can be risky in Vitest/Node.js environments as it can interfere with other native properties or event listeners on process. Removing this redundant mocking simplifies the test and avoids potential side-effects.

[mydd7]

Removed the stub. The suite is already skipIf non-win32, so the mock was redundant.