Improve diagnostic logging across MTP crash and IPC paths

[Evangelink]

Summary

Surgical improvements to internal logging across high-risk crash and diagnostic paths in Microsoft.Testing.Platform. The goal is to make it noticeably easier to diagnose problems and crashes from logs alone, without changing any public API.

Changes

File	Improvement
Helpers/UnhandledExceptionHandler.cs	Pattern-match e.ExceptionObject is Exception, route the typed exception through Log(LogLevel.Critical, msg, ex, Formatter) (structured sinks now get the object, not just a stringified message), and pass it into FailFast(msg, ex). Console output kept full-fidelity for backward-compat with acceptance tests.
Hosts/ServerTestHost.cs	Same exception-routing fix for OnCurrentDomainUnhandledException / OnTaskSchedulerUnobservedTaskException.
IPC/NamedPipeClient.cs	On IPC EOF the client called _environment.Exit(GenericFailure) with zero diagnostic output. Now writes a clear Console.Error.WriteLineAsync diagnostic naming the pipe and the most likely cause before exiting. Wrapped in try/catch so logging failures cannot shadow the original issue. [Embedded] type cannot take an ILogger without breaking MTP_MSBUILD_TASKS source-embedded compilation, so stderr is the pragmatic compromise.
IPC/NamedPipeServer.cs	Debug log on graceful client disconnect (was a silent return). Error log with pipe name, WasConnected and LoopTaskStatus before throwing on Dispose / DisposeAsync timeout.
Configurations/JsonConfigurationProvider.cs	Added null-safe LogDebugAsync / LogErrorAsync helpers. Logs: previously swallowed Path.GetFullPath failure; missing default config file (was silent return); JsonConfigurationFileParser.Parse failures with file path before rethrowing.
Configurations/ConfigurationManager.cs	Trace-level full-config dump wrapped in try/catch so I/O failures cannot break configuration loading.
Hosts/TestHostControllersTestHost.cs	Debug log when PID lookup InvalidOperationException is swallowed. Warning log on non-graceful exit including OS exit code, IPC-reported exit code (or <not received>), whether TestHostCompletedRequest was received, PID, and CancellationRequested.
Requests/TestHostTestFrameworkInvoker.cs	Session UID logged at Debug. Session warnings / failures previously only flowed to the output device; now also logged at Warning / Error with phase (CreateTestSession / CloseTestSession) and session UID.

Deliberately out of scope

• Microsoft.Testing.Extensions.HotReload has zero logging today — sizable instrumentation effort, deferred.
• ServerMode/JsonRpc/TcpMessageHandler.cs / MessageHandlerFactory.cs — connection loss, malformed headers and deserialization failures not logged. Substantial server-mode surface change, deferred.
• NamedPipeClient cannot accept an ILogger without breaking the [Embedded] / MTP_MSBUILD_TASKS source-embedded constraint.

Validation

• .\build.cmd -projects Microsoft.Testing.Platform.csproj — green for net8.0, net9.0, netstandard2.0.
• dotnet test Microsoft.Testing.Platform.UnitTests --filter "FullyQualifiedName~Configuration|FullyQualifiedName~UnhandledException|FullyQualifiedName~NamedPipe|FullyQualifiedName~ServerTestHost|FullyQualifiedName~TestHostControllers|FullyQualifiedName~TestHostTestFrameworkInvoker" — 75/75 pass.
• dotnet test Microsoft.Testing.Extensions.UnitTests — 334 pass, 4 skipped (platform-specific).
• Existing acceptance tests (UnhandledExceptionPolicyTests.cs) only assert message prefixes; verified the new structure still matches.

Notes

• No public API changes. All edits are internal to existing types.
• No .resx changes — MTP log messages are not localized.

[Copilot]

Pull request overview

This PR improves internal diagnostics across Microsoft.Testing.Platform crash, IPC, configuration, and test-host session paths without changing public API.

Changes:

• Routes typed exceptions into logger exception parameters for unhandled exception paths.
• Adds diagnostic logging for IPC disconnects, non-graceful test-host exits, config parse/load failures, and session warnings/failures.
• Makes trace-level configuration file dumping best-effort so diagnostic I/O failures do not break configuration loading.

Show a summary per file

File	Description
src/Platform/Microsoft.Testing.Platform/Requests/TestHostTestFrameworkInvoker.cs	Logs session UID and mirrors session warning/failure results to diagnostic logs.
src/Platform/Microsoft.Testing.Platform/IPC/NamedPipeServer.cs	Logs graceful client disconnects and dispose timeout diagnostics.
src/Platform/Microsoft.Testing.Platform/IPC/NamedPipeClient.cs	Emits a stderr diagnostic before exiting on IPC EOF.
src/Platform/Microsoft.Testing.Platform/Hosts/TestHostControllersTestHost.cs	Adds debug/warning details for PID lookup failures and non-graceful test-host exits.
src/Platform/Microsoft.Testing.Platform/Hosts/ServerTestHost.cs	Passes unhandled exceptions through logger exception parameters while preserving output-device text.
src/Platform/Microsoft.Testing.Platform/Helpers/UnhandledExceptionHandler.cs	Separates console text from structured log text and passes typed exceptions to logging/FailFast.
src/Platform/Microsoft.Testing.Platform/Configurations/JsonConfigurationProvider.cs	Adds null-safe debug/error logging for path resolution, missing default config, and parse failures.
src/Platform/Microsoft.Testing.Platform/Configurations/ConfigurationManager.cs	Wraps trace config dump in best-effort logging.

Copilot's findings

• Files reviewed: 8/8 changed files
• Comments generated: 0

[Copilot]

Copilot's findings

• Files reviewed: 8/8 changed files
• Comments generated: 0 new