[Flaky Test] Microsoft.Build.UnitTests.XMakeAppTests.GetCommandLineQuotedExe

**Flaky-test key** (automated de-duplication — do not edit):
```text
flaky-test-id: Microsoft.Build.UnitTests.XMakeAppTests.GetCommandLineQuotedExe
```

## Evidence

This test has been flagged as flaky by the automated flaky-test detector.

- **Distinct sources:** 3 (rolling `main` builds only)
- **Rolling build IDs:** [1464065](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1464065), [1475010](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1475010), [1481906](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1481906)
- **Total failures:** 4
- **Distinct error signatures:** 4 (indicating non-deterministic failure modes)
- **Legs:** FullOnWindows, FullOnWindows Release
- **TFMs:** net472
- **Assembly:** `Microsoft.Build.CommandLine.UnitTests`
- **First seen:** 2026-06-15
- **Last seen:** 2026-06-25
- **Sample build:** [1464065](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1464065)

### Representative error

```
Shouldly.ShouldAssertException : output
should contain (case insensitive comparison)
"D:\a\_work\1\s\artifacts\bin\Microsoft.Build.CommandLine.UnitTests\Debug\net472\MSBuild.exe /v:diag C:\Windows\system32\notepad.exe"
but was actually
"MSBuild version 18.9.0-ci-26315-01+4f9fffae9 for .NET Framework ..."
```

## Location

- **Fully-qualified name:** `Microsoft.Build.UnitTests.XMakeAppTests.GetCommandLineQuotedExe`
- **Assembly:** `Microsoft.Build.CommandLine.UnitTests`
- **Source:** `src/MSBuild.UnitTests/XMake_Tests.cs` (line ~1294)
- **Project:** `src/MSBuild.UnitTests/Microsoft.Build.CommandLine.UnitTests.csproj`

## Next steps

This test will be quarantined via `[ActiveIssue("https://github.com/dotnet/msbuild/issues/")]` (from `Microsoft.DotNet.XUnitV3Extensions`, namespace `Xunit`) — not `[Fact(Skip=...)]` — until the underlying nondeterminism is fixed. The quarantine pipeline (definition 344, `azure-pipelines/quarantine.yml`) will continue running this test on Windows/Linux/macOS across main's rolling builds to gather failure signal over time.

> Generated by [Flaky Test Triage](https://github.com/dotnet/msbuild/actions/runs/28288806840) · 405.3 AIC · ⊞ 34.9K · [◷](https://github.com/search?q=repo%3Adotnet%2Fmsbuild+is%3Aissue+%22gh-aw-workflow-call-id%3A+dotnet%2Fmsbuild%2Fflaky-test-detector.agent%22&type=issues)

Start with Microsoft.Build.UnitTests.XMakeAppTests.GetCommandLineQuotedExe in src/MSBuild.UnitTests/XMake_Tests.cs around line 1294, and compare its expected command-line output with the representative failure. Review how the test is quarantined through azure-pipelines/quarantine.yml, then investigate the nondeterminism and verify the test no longer fails across the Windows net472 rolling builds.

Written by the indexing model from the issue text.