fix: handle missing event calendar and simplify cancellation path

Author: cantpr09ram

app/dauphin/Utilities/EventManager.swift

@@ -19,17 +19,19 @@ import EventKit
     }
 
     /// 將你的模型轉成 EKEvent，給編輯器預填
-    func makeEKEvent(from ce: CalendarEvent) -> EKEvent {
+    /// Returns nil when no writable calendar is available.
+    func makeEKEvent(from ce: CalendarEvent) -> EKEvent? {
+        guard
+            let calendar = eventStore.defaultCalendarForNewEvents
+                ?? eventStore.calendars(for: .event).first
+        else { return nil }
+
         let ek = EKEvent(eventStore: eventStore)
         ek.title = ce.event
         ek.startDate = ce.startDate
         ek.endDate = ce.endDate
         ek.isAllDay = Calendar.current.isDate(ce.startDate, inSameDayAs: ce.endDate)
-        if let calendar = eventStore.defaultCalendarForNewEvents
-            ?? eventStore.calendars(for: .event).first
-        {
-            ek.calendar = calendar
-        }
+        ek.calendar = calendar
         return ek
     }
 }

app/dauphin/View/Other/Event/EventView.swift

@@ -28,8 +28,9 @@ struct EventView: View {
                     Button {
                         Task {
                             if await eventManager.requestWriteAccess() {
-                                editorItem = EditItem(
-                                    ekEvent: eventManager.makeEKEvent(from: event))
+                                if let ekEvent = eventManager.makeEKEvent(from: event) {
+                                    editorItem = EditItem(ekEvent: ekEvent)
+                                }
                             }
                         }
                     } label: {

app/dauphin/ViewModels/EventViewModel.swift

@@ -45,8 +45,6 @@ import OSLog
                 return delegate.events
             }
 
-            if Task.isCancelled { throw CancellationError() }
-
             if let err = parser.parserError { throw err }
 
             throw NSError(