npx vitest run hangs when running full test suites via Copilot CLI terminal

### Describe the bug

## Summary

Running `npx vitest run` for a full test suite hangs indefinitely when executed through the GitHub Copilot CLI terminal. The same command works fine in a regular PowerShell/cmd terminal.

## Environment

- **Tool**: GitHub Copilot CLI (VS Code)
- **OS**: Windows
- **Node**: v22.14.0
- **npm**: 10.9.2
- **Vitest**: v4.1.2

## Reproduction Steps

1. Open a Copilot CLI terminal session in VS Code
2. Run `npx vitest run`
3. Vitest starts, queues all test files, runs a few, then hangs with no further output
4. Typically nothing is seen piped back to the session window (the above has been deduced)

## What Works

- Running a **single test file** works fine: `npx vitest run some.test.ts`
- Running **batches of up to ~10 files** works fine
- Running with **JSON output to file** works and completes successfully:
```
npx vitest run --reporter=json --outputFile=test-results.json
```

## Root Cause

According to copilot which tried to diagnose this:
Vitest's default live reporter continuously rewrites terminal output using ANSI escape sequences (cursor movement, line clearing) for all queued files simultaneously. This high-volume ANSI output appears to overflow or deadlock the Copilot CLI's stdout pipe, causing the process to hang.

Redirecting output to a file bypasses the pipe entirely and the suite completes normally.

## Workaround

```bash
npx vitest run --reporter=json --outputFile=test-results.json
```

## Suggested Fix

### Affected version

vs code 1.120.0

### Steps to reproduce the behavior

1. Open a Copilot CLI terminal session in VS Code
2. Run `npx vitest run`
3. Vitest starts, queues all test files, runs a few, then hangs with no further output
4. Typically nothing is seen piped back to the session window (the above has been deduced)

### Expected behavior

See output of vitest

### Additional context

_No response_