Enforce warnings as errors for reflection-free acceptance builds

[Evangelink]

Summary

• promote compiler and MSBuild warnings to errors in ReflectionFree acceptance builds
• make the reflection-free mode own this contract instead of relying on the shared CLI default
• exercise the mode-specific warning settings in regular acceptance asset builds

Validation

• built Microsoft.Testing.TestInfrastructure.csproj with 0 warnings and 0 errors
• ran build.cmd -c Release -pack with 0 warnings and 0 errors
• ran MSTest.Acceptance.IntegrationTests.InconclusiveTests: 24 passed, including all 8 AotSourceGeneration cases

[Copilot]

🟢 Ready to approve

The focused changes correctly preserve existing behavior while making reflection-free warning enforcement explicit.

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Pull request overview

Enforces warning-free reflection-free acceptance builds through mode-specific MSBuild arguments.

Changes:

• Adds compiler and MSBuild warning promotion for AotSourceGeneration.
• Disables the shared warning default to verify the mode-owned contract.

File summaries

File	Description
AcceptanceSourceGen.cs	Adds reflection-free warning promotion arguments.
TestAssetFixtureBase.cs	Exercises mode-specific warning settings during asset builds.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Balanced

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[github-actions]

🧵 Parallel-safety audit — PR #10449

Nothing audited here touches process-global state, shared filesystem paths, or [ResourceLock] / [DoNotParallelize] declarations. Nothing to flag for parallel-safety.

The two changed files (AcceptanceSourceGen.cs, TestAssetFixtureBase.cs in test/Utilities/Microsoft.Testing.TestInfrastructure) are shared build-argument/test-asset helper infrastructure, not test classes: no [TestMethod]/[DataTestMethod], no [TestInitialize]/[ClassInitialize]/[AssemblyInitialize] lifecycle members, no [ResourceLock]/[DoNotParallelize]/[Parallelize] declarations, and no assembly parallelization configuration were added, removed, or modified. The changes only add a conditional warningsAsErrorsArg string to an existing MSBuild-argument builder and a warnAsError parameter to an existing DotnetCli.RunAsync call — no new mutation of environment variables, current directory, culture, console state, or shared static fields, and no new/changed filesystem paths.

No test assembly's parallelization state changed in this PR, so no scope table applies.

_{Re-run with /parallel-audit.}

🤖 Automated content by GitHub Copilot. Generated by the Parallel-safety audit on PR (on open / sync) workflow. · auto · 33.4 AIC · ⌖ 0.665 AIC · ⊞ 24.7K · [◷]( · ◷)