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

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

## 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.GetCommandLineQuotedExeOnPath`
- **Assembly:** `Microsoft.Build.CommandLine.UnitTests`
- **Source:** `src/MSBuild.UnitTests/XMake_Tests.cs` (line ~1317)
- **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 src/MSBuild.UnitTests/XMake_Tests.cs around XMakeAppTests.GetCommandLineQuotedExeOnPath and run the net472 test on Windows. Compare its command-line output with the representative failure and the other recorded error signatures. Done means the test is deterministic across rolling builds and no longer requires quarantine.

Written by the indexing model from the issue text.