Fix CI flakiness: async race conditions, disposal crash, and stdout truncation

[mmitche]

Summary

Fixes ~63% CI failure rate on the main branch caused by three independent race conditions.

Root Causes Identified

1. Parallel.For async void anti-pattern (TemplatePackageManager.cs)

Parallel.For(0, N, async (i) => ...) converts the lambda to async void. Parallel.For returns immediately after the synchronous portion of each iteration completes (up to the first await), not after the async work finishes. This leaves scanResults[] partially populated with nulls, causing OrderOfScanningIsCorrect test failures (expected sample99, got random values like sample69).

Fix: Replace with await Task.WhenAll(Enumerable.Range(...).Select(async ...))

2. GlobalSettings.FileChanged disposal race condition (GlobalSettings.cs)

FileChanged is an async void callback from a file watcher. The original Dispose() called _watcher.Dispose() before setting _disposed = true. The callback could fire between these two operations, hitting ObjectDisposedException on the SettingsChanged event handler. Since the exception is unhandled in async void, it crashes the entire xunit test runner process ΓÇö killing ALL Edge.UnitTests, not just the file watcher test.

Fix: Set _disposed = true before watcher disposal, add disposed check and ObjectDisposedException catch in FileChanged

3. Console output truncation in CLI commands (ExecutableCommand.cs)

SimpleConsoleLogger uses a background queue thread for console output. LoggerFactory.Dispose() drains the queue but the Console.Out pipe buffer may not be flushed before process exit. This causes mid-line output truncation in ValidateCommand_BasicTest integration tests.

Fix: Explicit Console.Out.Flush()/Console.Error.Flush() after logger factory disposal

Validation

10 consecutive CI passes on this branch (builds 1324248-1324572), compared to ~63% failure rate (20/32 failures) on the main branch over the same period.

Metric	Before	After
Failure rate	~63% (20/32)	0% (0/10)
Consecutive passes	1-2 max	10+
Test runner crashes	Frequent	None

Files Changed

• src/Microsoft.TemplateEngine.Edge/Settings/TemplatePackageManager.cs ΓÇö Parallel.For to Task.WhenAll
• src/Microsoft.TemplateEngine.Edge/BuiltInManagedProvider/GlobalSettings.cs ΓÇö Disposal ordering + FileChanged guards
• test/Microsoft.TemplateEngine.Edge.UnitTests/GlobalSettingsTests.cs ΓÇö Robustified TestFileWatcher event handler
• tools/Microsoft.TemplateEngine.Authoring.CLI/Commands/ExecutableCommand.cs ΓÇö Console flush after logger disposal