Hardened background work against disconnected circuits (#937)

app/MindWork AI Studio/Tools/TaskExtensions.cs

@@ -0,0 +1,53 @@
+namespace AIStudio.Tools;
+
+public static class TaskExtensions
+{
+    private static readonly ILogger LOGGER = Program.LOGGER_FACTORY.CreateLogger(nameof(TaskExtensions));
+
+    /// <summary>
+    /// Lets a task run on its own, but keeps an eye on how it ends.
+    /// </summary>
+    /// <remarks>
+    /// Use this wherever a task is started without awaiting it. Discarding one instead means that nobody
+    /// ever looks at its outcome: the task carries its exception until the garbage collector finalizes it,
+    /// and only then does it show up as an unobserved task exception — naming a task type, without any
+    /// hint at what was running. Around a circuit which is gone, that is the common case: components of a
+    /// reloaded or sleeping window still receive events and still schedule work.
+    /// </remarks>
+    /// <param name="task">The task to watch.</param>
+    /// <param name="context">What this task was doing, for the log entry.</param>
+    public static void Observe(this Task task, string context)
+    {
+        task.ContinueWith(finishedTask =>
+                LogFailure(finishedTask.Exception, context),
+                CancellationToken.None,
+            TaskContinuationOptions.OnlyOnFaulted | TaskContinuationOptions.ExecuteSynchronously,
+                TaskScheduler.Default);
+    }
+
+    private static void LogFailure(AggregateException? exception, string context)
+    {
+        if (exception is null)
+            return;
+
+        foreach (var innerException in exception.Flatten().InnerExceptions)
+        {
+            switch (innerException)
+            {
+                //
+                // The browser connection is gone, or the component was disposed while its work was still
+                // on its way. Neither is a defect: it is what a reload or a closed window looks like.
+                //
+                case JSDisconnectedException:
+                case ObjectDisposedException:
+                case OperationCanceledException:
+                    LOGGER.LogDebug("Background work '{Context}' stopped because its circuit was gone: {Reason}", context, innerException.Message);
+                    break;
+
+                default:
+                    LOGGER.LogError(innerException, "Background work '{Context}' failed.", context);
+                    break;
+            }
+        }
+    }
+}