Add workarounds and documentation for NativeAOT _BUILDCONFIG duplicate key error

[Copilot]

NativeAOT scenario runs in Azure DevOps fail with An item with the same key has already been added. Key: _BUILDCONFIG during MSBuild's out-of-process task host environment synchronization. The error occurs when environment variables are set at multiple levels (system, agent, pipeline), causing dictionary insertion to fail in OutOfProcTaskHostNode.UpdateEnvironmentForMainNode().

Workaround Script

• workarounds/nativeaot-environment-fix.sh - Detects Azure DevOps environments and applies MSBuildTaskHostDoNotUpdateEnvironment=1 to bypass environment sync
• Auto-detects TF_BUILD/AGENT_ID or presence of build config variables
• Includes comprehensive test suite with 6 scenarios

Documentation

• TROUBLESHOOTING.md - Root cause analysis, 4 workaround options, debugging techniques
• workarounds/azure-pipelines-example.yml - 4 pipeline integration patterns
• .github/ISSUE_TEMPLATE/build-failure.md - Structured issue reporting template

Usage

Pipeline-level fix (recommended):

variables:
  MSBuildTaskHostDoNotUpdateEnvironment: '1'

Or use detection script:

- bash: source workarounds/nativeaot-environment-fix.sh

This is a workaround-only solution. The underlying MSBuild issue should be fixed upstream to handle duplicate environment variable keys gracefully.

Original prompt

We have started hitting the following error in our main branch nativeaot_scenarios runs that run in Azure Devops.

[2025/12/04 21:04:20][INFO] Current dotnet directory: /__w/1/s/performance/CorrelationStaging/payload/dotnet
[2025/12/04 21:04:20][INFO] If more than one version exist in this directory, usually the latest runtime and sdk will be used.
[2025/12/04 21:04:20][INFO] $ dotnet msbuild /__w/1/s/performance/eng/performance/nativeaot_scenarios.proj /restore /t:PreparePayloadWorkItems /bl:/__w/1/s/performance/artifacts/log/x64_main_nativeaot_scenarios/PrepareWorkItemPayloads.binlog /p:ArtifactsLogDir=/__w/1/s/performance/artifacts/log/x64_main_nativeaot_scenarios
[2025/12/04 21:04:20][INFO] MSBuild version 18.3.0-preview-25603-106+5bb147b25 for .NET
[2025/12/04 21:04:22][INFO]   Determining projects to restore...
[2025/12/04 21:04:22][INFO]   Determining projects to restore...
[2025/12/04 21:04:23][INFO]   Restored /__w/1/s/performance/eng/performance/nativeaot_scenarios.proj (in 368 ms).
[2025/12/04 21:04:23][INFO]   All projects are up-to-date for restore.
[2025/12/04 21:04:24][INFO]   [2025/12/04 21:04:24][INFO] ----------------------------------------------
[2025/12/04 21:04:24][INFO]   [2025/12/04 21:04:24][INFO] Initializing logger 2025-12-04 21:04:24.042232
[2025/12/04 21:04:24][INFO]   [2025/12/04 21:04:24][INFO] ----------------------------------------------
[2025/12/04 21:04:24][INFO]   [2025/12/04 21:04:24][INFO] $ pushd "/__w/1/s/performance/CorrelationStaging/payload/performance/src/scenarios/emptyconsolenativeaot"
[2025/12/04 21:04:24][INFO]   [2025/12/04 21:04:24][INFO] $ dotnet new console --output app --no-restore --force --name emptyconsolenativeaot
[2025/12/04 21:04:24][INFO]   [2025/12/04 21:04:24][INFO] The template "Console App" was created successfully.
[2025/12/04 21:04:24][INFO]   [2025/12/04 21:04:24][INFO]
[2025/12/04 21:04:24][INFO]   [2025/12/04 21:04:24][INFO] $ popd
[2025/12/04 21:04:24][INFO]   [2025/12/04 21:04:24][INFO] $ pushd "/__w/1/s/performance/CorrelationStaging/payload/performance/src/scenarios/emptyconsolenativeaot"
[2025/12/04 21:04:24][INFO]   [2025/12/04 21:04:24][INFO] $ dotnet restore /__w/1/s/performance/CorrelationStaging/payload/performance/src/scenarios/emptyconsolenativeaot/app/emptyconsolenativeaot.csproj --packages /__w/1/s/performance/artifacts/packages /p:UseSharedCompilation=false /p:BuildInParallel=false /m:1 /p:EnableWindowsTargeting=true
[2025/12/04 21:04:25][INFO]   [2025/12/04 21:04:25][INFO]   Determining projects to restore...
[2025/12/04 21:04:27][INFO]   [2025/12/04 21:04:27][INFO]   Restored /__w/1/s/performance/CorrelationStaging/payload/performance/src/scenarios/emptyconsolenativeaot/app/emptyconsolenativeaot.csproj (in 1.04 sec).
[2025/12/04 21:04:27][INFO]   [2025/12/04 21:04:27][INFO] $ popd
[2025/12/04 21:04:27][INFO]   [2025/12/04 21:04:27][INFO] $ pushd "/__w/1/s/performance/CorrelationStaging/payload/performance/src/scenarios/emptyconsolenativeaot"
[2025/12/04 21:04:27][INFO]   [2025/12/04 21:04:27][INFO] $ dotnet publish /__w/1/s/performance/CorrelationStaging/payload/performance/src/scenarios/emptyconsolenativeaot/app/emptyconsolenativeaot.csproj --configuration Release /p:NuGetPackageRoot=/__w/1/s/performance/artifacts/packages/ /p:RestorePackagesPath=/__w/1/s/performance/artifacts/packages/ /p:UseSharedCompilation=false /p:BuildInParallel=false /m:1 --output /__w/1/s/performance/CorrelationStaging/payload/scenarios_out/emptyconsolenativeaot_aot --runtime linux-x64 --framework net10.0 /p:PublishAot=true /p:StripSymbols=true /p:IlcGenerateMstatFile=true /p:ObjCopyName=objcopy /p:EnableWindowsTargeting=true
[2025/12/04 21:04:28][INFO]   [2025/12/04 21:04:28][INFO]   Determining projects to restore...
[2025/12/04 21:04:33][INFO]   [2025/12/04 21:04:33][INFO]   Restored /__w/1/s/performance/CorrelationStaging/payload/performance/src/scenarios/emptyconsolenativeaot/app/emptyconsolenativeaot.csproj (in 3.94 sec).
[2025/12/04 21:04:33][INFO]   [2025/12/04 21:04:33][INFO] /__w/1/s/performance/CorrelationStaging/payload/dotnet/sdk/10.0.100-rc.3.25603.106/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.RuntimeIdentifierInference.targets(351,5): message NETSDK1057: You are using a preview version of .NET. See: https://aka.ms/dotnet-support-policy [/__w/1/s/performance/CorrelationStaging/payload/performance/src/scenarios/emptyconsolenativeaot/app/emptyconsolenativeaot.csproj]
[2025/12/04 21:04:37][INFO]   [2025/12/04 21:04:37][INFO]   emptyconsolenativeaot -> /__w/1/s/performance/CorrelationStaging/payload/performance/src/scenarios/emptyconsolenativeaot/app/bin/Release/net10.0/linux-x64/emptyconsolenativeaot.dll
[2025/12/04 21:04:39][INFO]   [2025/12/04 21:04:39][INFO] /__w/1/s/performance/artifacts/packages/microsoft.net.illink.tasks/10.0.0-rc.3.25603.106/build/Microsoft.NET.ILLink.targets(325,5): error MSB4018: The "ComputeManagedAssemblies" task failed unexpectedly. [/__w/1/s/performance/CorrelationStaging/payload/performance/src/...

</details>



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