[dotnet watch] Make application of changes always async

[tmat]

Application of changes has two code paths. When the process is suspended at a breakpoint we can't wait until the changes are applied in the process because the agent in the process can't execute until the process is resumed by the debugger. In that case we queued an update, assume it's succeeded and continue. If the process isn't suspended, we wait until the agent finishes applying the changes.

This distinction requires debugger API that tell us whether or not the process is suspended. This API is currently only available in VS, not in VS Code.
Rather than adding the API to VS Code, it is simpler to avoid synchronous waiting for completion of the apply operation altogether.
All we need to do on the code path that applies changes is to hook up task completions at various stages that aggregate and report results when apply operations complete.

[tmat]

@DustinCampbell ptal

[Copilot]

Pull request overview

This pull request refactors the hot reload change application mechanism to always be asynchronous, eliminating the distinction between suspended and non-suspended process states. Previously, the code had two paths: waiting synchronously for changes when the process wasn't suspended, or queueing updates asynchronously when it was suspended (at a breakpoint). This distinction required debugger APIs only available in Visual Studio. The new approach always queues updates asynchronously and reports results through fire-and-forget tasks that complete when operations finish.

Changes:

• Replaced synchronous apply operations with async fire-and-forget pattern that reports completion via task continuations
• Removed ApplyStatus enum and replaced return values with Task<Task<bool>> to support async completion tracking
• Eliminated isProcessSuspended parameter from apply methods, simplifying the API
• Updated message descriptors to reflect async timing (e.g., "C# and Razor changes applied in Xms" instead of per-project success messages)
• Fixed process exit code handling for Unix signals (SIGKILL tracking)

Reviewed changes

Copilot reviewed 25 out of 25 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/BuiltInTools/HotReloadClient/ApplyStatus.cs	Removed enum entirely as return type changed to bool
src/BuiltInTools/HotReloadClient/HotReloadClient.cs	Changed apply methods to return Task<Task<bool>> and added QueueUpdateBatch helper
src/BuiltInTools/HotReloadClient/DefaultHotReloadClient.cs	Refactored to use async queuing pattern with local completion tasks
src/BuiltInTools/HotReloadClient/Web/WebAssemblyHotReloadClient.cs	Updated to use new async queuing pattern
src/BuiltInTools/HotReloadClient/HotReloadClients.cs	Changed aggregation logic to work with async completion tasks
src/BuiltInTools/HotReloadClient/Utilities/ResponseFunc.cs	Changed from Action to Func to return results
src/BuiltInTools/HotReloadClient/Web/BrowserConnection.cs	Updated to return nullable response results
src/BuiltInTools/HotReloadClient/Web/AbstractBrowserRefreshServer.cs	Added generic result type support
src/BuiltInTools/HotReloadClient/Logging/LogEvents.cs	Updated log events for batch-based operations
src/BuiltInTools/Watch/HotReload/CompilationHandler.cs	Implemented fire-and-forget pattern for apply operations with stopwatch timing
src/BuiltInTools/Watch/HotReload/HotReloadDotNetWatcher.cs	Removed synchronous change handled logging, passes stopwatch to handlers
src/BuiltInTools/Watch/Process/RunningProject.cs	Added CompleteApplyOperationAsync to wrap and handle apply task exceptions
src/BuiltInTools/Watch/Process/ProcessRunner.cs	Enhanced signal tracking for Unix SIGKILL and Windows Ctrl+C
src/BuiltInTools/Watch/Context/EnvironmentOptions.cs	Removed isHotReloadEnabled parameter from timeout method
src/BuiltInTools/dotnet-watch/Watch/StaticFileHandler.cs	Added stopwatch for timing static asset changes
src/BuiltInTools/dotnet-watch/Program.cs	Simplified process runner initialization
src/BuiltInTools/Watch.Aspire/DotNetWatchLauncher.cs	Simplified process runner initialization
src/BuiltInTools/Watch/Microsoft.DotNet.HotReload.Watch.csproj	Added reference to ResponseFunc utility
src/BuiltInTools/Watch/UI/IReporter.cs	Updated message descriptors for async operations
test/dotnet-watch.Tests/TestUtilities/TestOptions.cs	Changed timeout to nullable
test/dotnet-watch.Tests/HotReload/RuntimeProcessLauncherTests.cs	Updated tests to use new message descriptors
test/dotnet-watch.Tests/HotReload/ApplyDeltaTests.cs	Updated tests to use new message descriptors and removed per-project assertions
test/dotnet-watch.Tests/Browser/BrowserTests.cs	Updated test to use new message descriptor
test/Microsoft.Extensions.DotNetDeltaApplier.Tests/HotReloadClientTests.cs	Removed suspended/non-suspended test distinction, updated to await async completion
test/Microsoft.TemplateEngine.Cli.UnitTests/ParserTests/InstallTests.cs	Removed trailing whitespace