[jonathanpeppers]

<GetAndroidDefineConstants/> only constructs an in-memory list, but its legacy base prevents in-process execution during MSBuild -mt builds. Use the existing multithreaded base and declare [MSBuildMultiThreadableTask] directly on the task. Constant generation is unchanged.

Add five focused cases for major/minor API levels, prior QPR constants, product-version sanitizing, and invalid input. The existing migration guard checks the attribute and base class. No linked issue.

Validation

Validation used an isolated .NET 11 SDK (11.0.100-rc.2.26504.105) and temporary .NET 11 package overrides, including an explicit runtime-pack version. These overrides are not part of this PR.

• .\dotnet-local.cmd build Microsoft.Android.slnx -t:BuildDotNet -c Release -nr:false -v:minimal - passed; 92 warnings, no errors.
• .\dotnet-local.cmd build src\Xamarin.Android.Build.Tasks\Tests\Xamarin.Android.Build.Tests\Xamarin.Android.Build.Tests.csproj -c Release --no-restore -p:BuildProjectReferences=false -nr:false -v:minimal - passed; no warnings or errors.
• .\dotnet-local.cmd test bin\TestRelease\net10.0\Xamarin.Android.Build.Tests.dll --filter "FullyQualifiedName~GetAndroidDefineConstantsTests|FullyQualifiedName~MultiThreadedMigrationTests" - passed, 6/6 tests, none skipped.

Separate two-project probes passed in ordinary and strict -m:2 -mt -nr:false -warnaserror:MSB4286,MSB4287,MSB4288 builds. binlogtool confirmed two task calls without task-host routing; ordered output items and metadata matched across modes. A Release APK build also confirmed .NET 11 SDK, reference, ILLink, MonoTargets, CoreCLR, and CoreLib selections.

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Pull Request
title and
description
should follow the
commit-messages.md workflow documentation, and in particular should include:

• Useful description of why the change is necessary.
• Links to issues fixed
• Unit tests

[Copilot]

🟢 Approval recommended

The narrow migration preserves generation logic, has focused test coverage and reported strict multithreaded validation, and has no unresolved review findings.

No open issues 🎉

What changed in this PR

This PR enables GetAndroidDefineConstants to run in-process during multithreaded MSBuild builds without changing constant generation.

Changes:

• Switches the task to MultithreadedAndroidTask and declares [MSBuildMultiThreadableTask] directly.
• Adds five test cases covering major/minor API levels, prior QPR constants, product-version sanitizing, and invalid input.

File	Description
src/​Xamarin.Android.Build.Tasks/​Tests/​Xamarin.Android.Build.Tests/​Tasks/​GetAndroidDefineConstantsTests.cs	Adds focused constant-generation and invalid-input tests.
src/​Xamarin.Android.Build.Tasks/​Tasks/​GetAndroidDefineConstants.cs	Enables in-process execution through the existing multithreaded task infrastructure.

_{Review effort: Balanced}

[jonathanpeppers]

@dalexsoto review

[dalexsoto]

Reviewed the complete 2-file task/test change and the relevant task base, MSBuild environment/routing, production consumers and source tests. GetAndroidDefineConstants retains stateless execution, ordered constants, parsing and MSBuild integration. No high-confidence blockers remain in the bounded static review.