[Repo Assist] fix: guard findFiles against out-of-boundary directory paths

[github-actions]

🤖 This is an automated draft PR from Repo Assist.

Problem

findFiles() in lib/utils.js contains a subtle bug that only manifests when path.relative(workspaceRoot, fileDir) returns an absolute path rather than a relative one.

On Windows, path.relative between two paths on different drives returns an absolute path (e.g. path.relative("C:\\ws", "D:\\other") → "D:\\other"). When this is passed to findFiles, path.resolve(parent, directory) treats it as absolute and ignores parent entirely. The loop then walks up from D:\other all the way to D:\ — the loop's parent === currentDir stop condition is never satisfied because parent is on C:\.

The same issue can occur on Unix if directory happens to be an absolute path for any other reason.

Fix

Add an early-exit guard at the start of findFiles: if the resolved starting directory is not within parent (i.e. not equal to parent and not a descendant of parent), return null immediately.

Also, use the pre-resolved resolvedParent instead of the raw parent string in the loop's stop condition, to be consistent and correct regardless of whether parent was passed with a trailing separator.

// New guard (added before the walk loop)
if (resolvedStart !== resolvedParent &&
    !resolvedStart.startsWith(resolvedParent + path.sep)) {
    return null;
}
```

## Test Status

New test added to `test/unit.test.js`:

```
✔ findFiles (8/8 passing) ✅
  including:
  ✔ returns null when directory is outside parent (simulated cross-drive path)

node --check lib/utils.js: OK ✅
node --check extension.js: OK ✅

No CI workflow exists in this repository; all checks are manual.

Impact

• Zero behaviour change for the common case (all paths on the same drive / filesystem)
• Prevents unbounded upward walks on Windows multi-drive setups
• Makes the stop condition more robust by comparing resolved paths throughout

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