[ci-scan] Test failure: System.Tests.DoubleTests.Parse_CustomSigns fails for surrogate-pair custom sign #135014

Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1618965
Build error leg or test failing: windows-x86 Debug Libraries_CheckedCoreCLR-System.Tests.DoubleTests.Parse_CustomSigns
Pull request: #134960

Parse_CustomSigns was added on main by #134857 (merged 2026-09-30). It fails in PR builds that don't touch libraries. Before 2026-10-01, Build Analysis wrongly matched these failures to #133999 through an overly broad IsIanaIdTest pattern. That pattern has since been removed, and the failures now show as unmatched. Kusto TestKnownIssues attributes Parse_CustomSigns failures to #133999 in 44 builds across more than 20 PRs, including #134857, #134978, #134960, #134668, #134494, #134875, #134993 and #134991.

The failing row uses a supplementary-plane (surrogate pair) custom positive sign. The log console renders it as ??.

Error Details

System.Tests.DoubleTests.Parse_CustomSigns(value: "??Infinity", positiveSign: "??", negativeSign: "-", expectedSuccess: True, expected: ∞) [FAIL]
  Assert.Equal() Failure: Values differ
  Expected: True
  Actual:   False
  Stack Trace:
    /_/src/libraries/System.Runtime/tests/System.Runtime.Tests/System/DoubleTests.cs(1446,0): at System.Tests.DoubleTests.Parse_CustomSigns(String value, String positiveSign, String negativeSign, Boolean expectedSuccess, Double expected)
       at InvokeStub_DoubleTests.Parse_CustomSigns(Object, Span`1)

The theory row is value: "\U00010400Infinity" (𐐀Infinity) with positiveSign: "\U00010428" (𐐨). double.TryParse returns false where the test expects true.

Configuration: net11.0-windows-Debug-x86-coreclr_checked-Windows.10.Amd64.Open, Helix job e45775cb-103a-475f-9f07-250ab1a48c98, work item System.Runtime.Tests.

Error Message

{
  "ErrorMessage": ["System.Tests.DoubleTests.Parse_CustomSigns(value: ", "Assert.Equal() Failure: Values differ", "Expected: True", "Actual:   False"],
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1618965
Error message validated: [System.Tests.DoubleTests.Parse_CustomSigns(value: Assert.Equal() Failure: Values differ Expected: True Actual: False]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 10/1/2026 12:40:48 PM UTC

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