Test failure: System.Threading.Tests.MutexTests.NameOptionsApiCompatibilityTest #135888

Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1635689
Build error leg or test failing: WasmTestOnWasmtime-CLR-ST-System.Threading.Tests - System.Threading.Tests.MutexTests.NameOptionsApiCompatibilityTest
Pull request: #135778

Tracking issue: #135887. Regression from #135778: on Unix, a named mutex created without NamedWaitHandleOptions is now user-scoped by default, so reopening it with CurrentUserOnly = false creates a new mutex. Fails deterministically on WASI, browser (CoreCLR and Mono), macOS and Linux.

Error Details

[FAIL] System.Threading.Tests.MutexTests.NameOptionsApiCompatibilityTest(namePrefix: "")
Assert.False() Failure
Expected: False
Actual:   True
   at System.Threading.Tests.MutexTests.NameOptionsApiCompatibilityTest(String namePrefix)
   at System.Reflection.InstanceCalliHelper.Call( fn, Object o, Object arg1)
   at System.Reflection.IntrinsicInvokeHelper.Instance_Void_1Obj(IntPtr fn, Object obj, IntPtr* args, RuntimeType _)

Error Message

{
  "ErrorMessage": [
    "NameOptionsApiCompatibilityTest(namePrefix:",
    "Assert.False() Failure"
  ],
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1635689
Error message validated: [NameOptionsApiCompatibilityTest(namePrefix: Assert.False() Failure]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 10/15/2026 7:25:14 PM UTC

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