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

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

## Evidence

Failing intermittently across 3 distinct sources (1 approved PR + 2 rolling `main` builds) on **CoreOnMac** with multiple distinct error signatures (timeouts).

- **Assembly:** `Microsoft.Build.CommandLine.UnitTests`
- **Class:** `Microsoft.Build.UnitTests.XMakeAppTests`
- **Method:** `LoggerThrowsMemberAccessExceptionWhenClassIsInvalid`
- **Distinct sources:** 3 (PR [#14543](https://github.com/dotnet/msbuild/pull/14543) + rolling builds [1533317](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1533317), [1537002](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1537002))
- **Legs:** CoreOnMac
- **TFMs:** net11.0
- **First seen:** 2026-07-28
- **Last seen:** 2026-08-03
- **Error hashes:** 4 distinct (`6982e6fd`, `11a572e5`, `1e3c1d4c`, `aa16386d`)
- **Sample error:** `System.TimeoutException : Test failed due to timeout: process 23412 is active for more than 30 sec.`
- **Sample build:** [1529449](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1529449)

## Source location

`src/MSBuild.UnitTests/XMake_Tests.cs`

## Notes

This test will be quarantined via `[ActiveIssue("")]` (from `Microsoft.DotNet.XUnitV3Extensions`, namespace `Xunit`) once this issue is confirmed open. The quarantine pipeline (def 344) will gather further signal. A real fix is tracked separately.

> [!WARNING]
>
> Firewall blocked 1 domain
>
> The following domain was blocked by the firewall during workflow execution:
>
> - `southcentralus0.in.applicationinsights.azure.com`
>
> To allow these domains, add them to the `network.allowed` list in your workflow frontmatter:
>
> ```yaml
> network:
> allowed:
> - defaults
> - "southcentralus0.in.applicationinsights.azure.com"
> ```
>
> See [Network Configuration](https://github.github.com/gh-aw/reference/network/) for more information.
>
>

> Generated by [Flaky Test Triage](https://github.com/dotnet/msbuild/actions/runs/30814926510) · sonnet46 · 122.4 AIC · ⌖ 6.59 AIC · ⊞ 15K · [◷](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)

Open src/MSBuild.UnitTests/XMake_Tests.cs and locate XMakeAppTests.LoggerThrowsMemberAccessExceptionWhenClassIsInvalid. Review the existing flaky-test evidence and the ActiveIssue guidance from Microsoft.DotNet.XUnitV3Extensions, then quarantine this test with the issue URL. Done means the test is marked for quarantine and the relevant test project still builds and runs.

Written by the indexing model from the issue text.