[Flaky Test] Microsoft.Build.Tasks.UnitTests.WriteLinesToFile_Tests.NonTransactionalModeCausesDataLoss

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

## Evidence

- **Distinct sources:** 3 (0 PRs + 3 rolling main builds)
- **Rolling builds:** [1496519](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1496519), [1506834](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1506834), [1514373](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1514373)
- **Legs:** FullOnWindows, FullOnWindows Release
- **TFM:** net472
- **Assembly:** Microsoft.Build.Tasks.UnitTests
- **First seen:** 2026-07-07 | **Last seen:** 2026-07-17
- **Error hashes:** 2 distinct (24ca1695, 321cf66e) — multiple distinct failure signatures confirm non-determinism
- **Sample build:** [1496519](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1496519)

**Sample error:**
```
Microsoft.Build.Exceptions.BuildAbortedException: Build was canceled. Failed to successfully launch or connect to a child MSBuild.exe process.
```

## Notes

This test will be quarantined via `[ActiveIssue("https://github.com/dotnet/msbuild/issues/")]` (from `Microsoft.DotNet.XUnitV3Extensions`, namespace `Xunit`) until the underlying nondeterminism is fixed.

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> Generated by [Flaky Test Triage](https://github.com/dotnet/msbuild/actions/runs/29643670790) · 114.5 AIC · ⌖ 4.91 AIC · ⊞ 13.5K · [◷](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)

Locate Microsoft.Build.Tasks.UnitTests.WriteLinesToFile_Tests.NonTransactionalModeCausesDataLoss in the Microsoft.Build.Tasks.UnitTests assembly and run it on the affected Windows net472 configuration. Inspect the non-transactional test behavior and the BuildAbortedException failures; done means the test is deterministic and no longer needs the ActiveIssue quarantine.

Written by the indexing model from the issue text.