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

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

## 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.GetCommandLine`
- **Assembly:** `Microsoft.Build.CommandLine.UnitTests`
- **Source:** `src/MSBuild.UnitTests/XMake_Tests.cs` (line ~1279)
- **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.GetCommandLine in src/MSBuild.UnitTests/XMake_Tests.cs around line 1279, and review its project file and the representative output mismatch. Use the quarantine runs to compare the four failure signatures across Windows net472 builds. Done means the test no longer exhibits nondeterministic failures and the quarantine is no longer needed.

Written by the indexing model from the issue text.