Summary

Main's Pack preview step fails with CP0021 against the 1.1.0 package baseline: the recently merged testing-stack PR tightened UseRealFor<TService, TImplementation>'s TService constraint from notnull to class. The PublicAPI analyzers don't track generic constraints, so the PR build was green - APICompat at pack time caught it.

The constraint change is kept and declared as an intentional divergence via CompatibilitySuppressions.xml (same mechanism as the MySql per-TFM suppression), because:

• No valid caller can break: TImplementation : class, TService already made a non-reference TService uninstantiable (a class cannot derive from a struct; interfaces satisfy the class constraint).
• Reverting to notnull is not implementable with the lazy-factory design: AutoMocker's Use<TService>(Func<AutoMocker, TService>) cannot be bound when TService is merely notnull - explicit type arguments fail with CS0452 against the class-constrained Mock<TService> overload, and inference silently binds the wrong overload (registering the delegate itself as a service; test-verified). The alternative would regress UseRealFor to eager creation, losing the lazy + auto-disposal semantics.

The full analysis is preserved as a comment in the suppression file.

Verification

• dotnet pack src/Vulthil.xUnit -c Release against the 1.1.0 baseline: green (previously CP0021 x4).
• tests/Vulthil.SharedKernel.Tests (incl. the UseRealFor auto-disposal and dependency-visibility tests): 36/36 passing, both TFMs.
• Both alternative fixes were implemented and tested before choosing the suppression: the explicit-delegate + notnull variant compiles but binds the wrong overload (2 test failures); explicit type arguments fail with CS0452.

Backport to v1.0: no - repairs the main-line package baseline only.