@files fails on directories with too many files

### Describe the bug

Hey Team 😊

@files is broken when Copilot CLI is started in a directory with too many files/subfolders. It used to work but I can't really remember what version broke the fuzzy find.

I have to tell you guys that Gemini CLI works fine with the same large folder, so it has to do with the way Copilot CLI is handling large folders.

I am not sure how to provide an example here...

### Affected version

GitHub Copilot CLI 1.0.39.

### Steps to reproduce the behavior

_No response_

### Expected behavior

_No response_

### Additional context

_No response_

No files, tests, or reproduction steps are named. Start by reproducing the @files failure in GitHub Copilot CLI 1.0.39 from a directory with many files and subfolders, then trace the fuzzy-find handling for large directories. Done means @files works reliably in that environment without regressing normal directory searches.

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