fix: error when playing notification sounds in quick succession

docs/changelog/v0.2.10.md

@@ -13,6 +13,7 @@ Follow-up patch release for v0.2.9 addressing auto-updater regressions, adding a
 - Fix pre-update backup failing when a Serilog-held log file is locked — `UpdateBackupService` now enumerates files manually, skips the `logs/` directory and `.log` files, and logs-and-continues on `IOException`/`UnauthorizedAccessException` instead of aborting the whole backup
 - Simplify update progress dispatch — remove redundant `Application.Invoke` wrappers around progress updates that are already called from the UI thread (introduced while fixing the freeze above)
 - Fix cursor position being reset to the start of the line when auto-completing commands in the CLI app — insertion point is now moved to the end of the completed text
+- Fix notification sounds crashing or being silently dropped when several arrive in quick succession — playback is now serialized through a semaphore that's held for the duration of each sound (using `PlaybackFinished` with a 10s safety timeout) and always released in `finally`, so back-to-back notifications queue up and play in order instead of racing the underlying audio player (fixes #20)
 
 ## Refactoring
 

src/EchoHub.Client/Services/NotificationSoundService.cs

@@ -6,7 +6,11 @@ namespace EchoHub.Client.Services;
 
 public class NotificationSoundService
 {
+    // Safety net: if PlaybackFinished never fires we don't want to block future notifications forever.
+    private static readonly TimeSpan PlaybackTimeout = TimeSpan.FromSeconds(10);
+
     private readonly Player _player = new();
+    private readonly SemaphoreSlim _lock = new(1, 1);
     private readonly NotificationConfig _config;
     private string? _resolvedSoundPath;
 
@@ -41,18 +45,31 @@ public async Task PlayTestAsync()
 
     private async Task PlayInternal()
     {
+        await _lock.WaitAsync();
+
+        // _player.Play returns as soon as playback starts, so we wait on PlaybackFinished
+        // to hold the lock for the duration of the sound. A one-shot handler + timeout
+        // keeps the finally release robust: never-fires → timeout; fires twice → ignored
+        // (TrySetResult); handler throws → caller's catch still runs finally.
+        var completion = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
+        void OnFinished(object? s, EventArgs e) => completion.TrySetResult();
+        _player.PlaybackFinished += OnFinished;
+
         try
         {
-            if (_player.Playing)
-                await _player.Stop();
-
             await _player.SetVolume(_config.Volume);
             await _player.Play(_resolvedSoundPath!);
+            await Task.WhenAny(completion.Task, Task.Delay(PlaybackTimeout));
         }
         catch (Exception ex)
         {
             Log.Warning(ex, "Failed to play notification sound");
         }
+        finally
+        {
+            _player.PlaybackFinished -= OnFinished;
+            _lock.Release();
+        }
     }
 
     private void ResolveSoundPath()