[Flaky Test] Microsoft.Build.Coordinator.UnitTests.CoordinatorServer_Tests.ConcurrentClients_AllReceiveGrants

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

## Evidence

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

- **Distinct sources:** 8 (4 PRs + 4 rolling `main` builds)
- **Affected PRs:** #14079, #14104, #14130, #14135
- **Rolling build IDs:** [1472231](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1472231), [1472331](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1472331), [1477803](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1477803), [1478840](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1478840)
- **Total failures:** 9
- **Legs:** CoreOnWindows, FullOnWindows, FullOnWindows Release
- **TFMs:** net472
- **Assembly:** `MSBuild.Coordinator.UnitTests`
- **First seen:** 2026-06-17
- **Last seen:** 2026-06-24
- **Sample build:** [1469611](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1469611)

### Representative error

```
System.IO.IOException : The semaphore timeout period has expired.
```

## Location

- **Fully-qualified name:** `Microsoft.Build.Coordinator.UnitTests.CoordinatorServer_Tests.ConcurrentClients_AllReceiveGrants`
- **Assembly:** `MSBuild.Coordinator.UnitTests`
- **Source:** `src/MSBuild.Coordinator.UnitTests/CoordinatorServer_Tests.cs` (line ~225)
- **Project:** `src/MSBuild.Coordinator.UnitTests/MSBuild.Coordinator.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.Coordinator.UnitTests/CoordinatorServer_Tests.cs around line 225 and the named ConcurrentClients_AllReceiveGrants test, then review its project file and the representative net472 Windows failure. Use the quarantine pipeline details to observe further runs; done means the semaphore-timeout nondeterminism is fixed and the test no longer needs quarantine.

Written by the indexing model from the issue text.