More granular websocket error handling

QueueCube/Backend/API.swift

@@ -162,8 +162,7 @@ struct API
                     
                     websocketTask.sendPing { error in
                         if let error {
-                            print("Ping error: \(error). Trying to reconnect.")
-                            continuation.yield(.error(.websocketError(error)))
+                            notifyError(error, continuation: continuation)
                             websocketTask = spawnWebsocketTask(with: continuation)
                         } else {
                             continuation.yield(.event(Event(type: .receivedWebsocketPong)))
@@ -204,14 +203,28 @@ struct API
                     }
                 }
             } catch {
-                print("Websocket Error: \(error)")
-                continuation.yield(.error(API.Error.websocketError(error)))
+                notifyError(error, continuation: continuation)
             }
         }
         
         return websocketTask
     }
     
+    private func notifyError(_ error: any Swift.Error, continuation: AsyncStream<StreamEvent>.Continuation) {
+        print("Websocket Error: \(error)")
+        var shouldNotifyObservers = true
+        let nsError = error as NSError
+        if nsError.code == 53 {
+            // This is a "connection abort", caused by backgrounding.
+            // Don't notify UI, just silently reconnect.
+            shouldNotifyObservers = false
+        }
+        
+        if shouldNotifyObservers {
+            continuation.yield(.error(.websocketError(error)))
+        }
+    }
+    
     private func request() -> RequestBuilder {
         RequestBuilder(url: baseURL)
     }
@@ -247,6 +260,7 @@ struct API
             
             // Private UI events
             case receivedWebsocketPong
+            case websocketReconnected
         }
     }
 }