[Keboo]

Summary

Fix teardown failures observed when running ten non-interactive UI tests concurrently in MaterialDesignInXAML/MaterialDesignInXamlToolkit#4103. The failing run reported 17 gRPC Cancelled exceptions from App.DisposeAsync after test bodies and recorder success checks completed: https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit/actions/runs/39060871422/job/117478381849.

• Increase the shutdown RPC allowance from one second to ten seconds for both disposal paths.
• Handle and log gRPC cancellation only when the local shutdown timeout has expired. Preserve unexpected RPC cancellations, other RPC failures, and server error replies.
• Replace CPU-intensive process polling with bounded WaitForExit / WaitForExitAsync on the existing process instance. Retain forced termination and confirm exit with another bounded wait.
• Preserve remote log cleanup even if process cleanup throws.
• Test only public APIs: real hosts started with App.StartRemote, lifecycle behavior through IApp, and remote setup through RemoteExecute. No friend assemblies, internal casts, reflection into implementation details, or transport mocks.
• Add Microsoft.CodeAnalysis.BannedApiAnalyzers to every project with a shared BannedSymbols.txt, banning InternalsVisibleToAttribute as an RS0030 build error.
• Align MSTest adapter 4.4.1 with framework 4.5.1: the mismatch prevented discovery entirely.
• Document disposal behavior and the public-API-only testing policy.

The server's existing 500 ms delayed shutdown/protocol is unchanged. Toolkit window activation and its package reference are also unchanged; consuming a published fixed build remains separate work.

Validation

• dotnet build XAMLTest.slnx -c Release: succeeded with no warnings or errors.
• dotnet test XAMLTest.Tests\XAMLTest.Tests.csproj -c Release --no-restore --filter FullyQualifiedName~AppDisposalTests --logger "console;verbosity=minimal": all 8 public-API cases passed.
• Covers synchronous/asynchronous disposal of already-exited hosts, graceful slow exit, forced termination of a host blocked in its Exit event, nonblocking asynchronous disposal, and three batches of ten concurrent real hosts per disposal mode (60 hosts total).
• Temporary negative build probes verified that both handwritten and SDK-generated InternalsVisibleTo attributes fail with RS0030. Probes were removed afterward.

The former implementation-level mocked RPC tests were removed rather than bypassing the public API boundary. The public lifecycle tests do not claim deterministic coverage of individual transport exception branches.