Fix race condition on app swap that would cause ndb to remain closed

Signed-off-by: Daniel D’Aquino <daniel@daquino.me>

damus/ContentView.swift

@@ -135,6 +135,7 @@ struct ContentView: View {
     @StateObject var navigationCoordinator: NavigationCoordinator = NavigationCoordinator()
     @AppStorage("has_seen_suggested_users") private var hasSeenOnboardingSuggestions = false
     let sub_id = UUID().description
+    @State var damusClosingTask: Task<Void, Never>? = nil
     
     // connect retry timer
     let timer = Timer.publish(every: 1, on: .main, in: .common).autoconnect()
@@ -478,6 +479,8 @@ struct ContentView: View {
         }
         .onReceive(NotificationCenter.default.publisher(for: UIApplication.willEnterForegroundNotification)) { obj in
             print("txn: 📙 DAMUS ACTIVE NOTIFY")
+            Task {
+                await damusClosingTask?.value  // Wait for the closing task to finish before reopening things, to avoid race conditions
                 if damus_state.ndb.reopen() {
                     print("txn: NOSTRDB REOPENED")
                 } else {
@@ -502,7 +505,6 @@ struct ContentView: View {
                         }
                     }
                 }
-            Task {
                 await damus_state.purple.check_and_send_app_notifications_if_needed(handler: home.handle_damus_app_notification)
             }
         }
@@ -511,7 +513,7 @@ struct ContentView: View {
             switch phase {
             case .background:
                 print("txn: 📙 DAMUS BACKGROUNDED")
-                Task { @MainActor in
+                damusClosingTask = Task { @MainActor in
                     await damus_state.nostrNetwork.close()  // Close ndb streaming tasks before closing ndb to avoid memory errors
                     damus_state.ndb.close()
                 }
@@ -521,8 +523,11 @@ struct ContentView: View {
                 break
             case .active:
                 print("txn: 📙 DAMUS ACTIVE")
+                Task {
+                    await damusClosingTask?.value  // Wait for the closing task to finish before reopening things, to avoid race conditions
                     damus_state.nostrNetwork.connect()
                     damus_state.nostrNetwork.ping()
+                }
             @unknown default:
                 break
             }