Remove diagnostic instrumentation

Remove all temporary diagnostic artifacts added during hang investigation:
- Instrumented xUnit DLLs and ReplaceXunitWithInstrumented MSBuild targets
- DiagnosticExceptionTracing.cs module initializer
- DOTNET_RuntimeAsync=0 CI workaround (was wrong hypothesis)
- xunit-runtest-diag.log artifact collection glob

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: ericstj

.github/workflows/ci-build-test.yml

@@ -61,11 +61,6 @@ jobs:
       run: make build CONFIGURATION=${{ matrix.configuration }}
 
     - name: 🧪 Test
-      # TODO: Remove DOTNET_RuntimeAsync=0 workaround once the .NET runtime fix is available.
-      # Tracked by: https://github.com/dotnet/runtime/issues/126325
-      # xUnit v3 test host hangs intermittently on .NET 10 with RuntimeAsync enabled.
-      env:
-        DOTNET_RuntimeAsync: "0"
       run: make test CONFIGURATION=${{ matrix.configuration }}
 
     - name: 🧪 AOT Compatibility
@@ -86,7 +81,6 @@ jobs:
         name: testresults-${{ matrix.os }}-${{ matrix.configuration }}
         path: |
           artifacts/testresults/**
-          **/xunit-runtest-diag.log
 
   publish-coverage:
     if: github.actor != 'dependabot[bot]'

tests/Common/InstrumentedXunit/xunit.v3.common.dll

@@ -62,15 +62,4 @@
     <ProjectReference Include="..\ModelContextProtocol.ConformanceServer\ModelContextProtocol.ConformanceServer.csproj" />
   </ItemGroup>
 
-  <!-- TEMPORARY: Replace xUnit DLLs with instrumented versions that add tracing to
-       TestRunner.RunTest to diagnose intermittent hang where finished TCS is never signaled.
-       Remove this target once the root cause is identified. -->
-  <Target Name="ReplaceXunitWithInstrumented" AfterTargets="Build"
-          Condition="Exists('$(MSBuildThisFileDirectory)..\Common\InstrumentedXunit\xunit.v3.core.dll')">
-    <Copy SourceFiles="$(MSBuildThisFileDirectory)..\Common\InstrumentedXunit\xunit.v3.core.dll"
-          DestinationFolder="$(OutputPath)" OverwriteReadOnlyFiles="true" SkipUnchangedFiles="false" />
-    <Copy SourceFiles="$(MSBuildThisFileDirectory)..\Common\InstrumentedXunit\xunit.v3.common.dll"
-          DestinationFolder="$(OutputPath)" OverwriteReadOnlyFiles="true" SkipUnchangedFiles="false" />
-  </Target>
-
 </Project>

tests/Common/InstrumentedXunit/xunit.v3.core.dll

@@ -98,15 +98,4 @@
     </Content>
   </ItemGroup>
 
-  <!-- TEMPORARY: Replace xUnit DLLs with instrumented versions that add tracing to
-       TestRunner.RunTest to diagnose intermittent hang where finished TCS is never signaled.
-       Remove this target once the root cause is identified. -->
-  <Target Name="ReplaceXunitWithInstrumented" AfterTargets="Build"
-          Condition="Exists('$(MSBuildThisFileDirectory)..\Common\InstrumentedXunit\xunit.v3.core.dll')">
-    <Copy SourceFiles="$(MSBuildThisFileDirectory)..\Common\InstrumentedXunit\xunit.v3.core.dll"
-          DestinationFolder="$(OutputPath)" OverwriteReadOnlyFiles="true" SkipUnchangedFiles="false" />
-    <Copy SourceFiles="$(MSBuildThisFileDirectory)..\Common\InstrumentedXunit\xunit.v3.common.dll"
-          DestinationFolder="$(OutputPath)" OverwriteReadOnlyFiles="true" SkipUnchangedFiles="false" />
-  </Target>
-
 </Project>