fix: preserve cached events when a calendar has a per-source sync error

Root cause: mergeIntoCache() unconditionally evicted every event in the
fetched date range, even for calendars whose sync failed. Those calendars'
events were removed and never restored, so the calendar appeared to vanish.

Fix:
- SyncError now decodes calendarId from the server's "calendar_id" field
  (added server-side in e0ea16f but not yet read by iOS).
- mergeIntoCache() gains a keepKeysInRange parameter: events from failed
  calendars are retained (not evicted) even within the fetch window.
- loadEvents() and prefetchBackground() compute the failed keys from the
  syncErrors list and pass them to mergeIntoCache.

Result: when CalDAV / Google / HA sync fails for a specific calendar, the
user sees stale-but-correct events alongside the existing error banner,
instead of a completely empty calendar with no explanation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Calendarr iOS.xcodeproj/project.pbxproj

@@ -511,7 +511,7 @@
 					"$(inherited)",
 					"@executable_path/Frameworks",
 				);
-				MARKETING_VERSION = 2.8;
+				MARKETING_VERSION = 2.9;
 				PRODUCT_BUNDLE_IDENTIFIER = com.scarriffleservices.calendarr.ios;
 				PRODUCT_NAME = "Calendarr iOS";
 				STRING_CATALOG_GENERATE_SYMBOLS = YES;
@@ -555,7 +555,7 @@
 					"$(inherited)",
 					"@executable_path/Frameworks",
 				);
-				MARKETING_VERSION = 2.8;
+				MARKETING_VERSION = 2.9;
 				PRODUCT_BUNDLE_IDENTIFIER = com.scarriffleservices.calendarr.ios;
 				PRODUCT_NAME = "Calendarr iOS";
 				STRING_CATALOG_GENERATE_SYMBOLS = YES;

Calendarr iOS/Models/CalEvent.swift

@@ -25,6 +25,7 @@ struct EventPerson: Hashable {
 /// succeeded, just not every source within it.
 struct SyncError: Hashable {
     let source: String
+    let calendarId: String?   // nil on older server responses without calendar_id
     let name: String
     let message: String
 
@@ -34,7 +35,8 @@ struct SyncError: Hashable {
             let name    = json["name"]    as? String,
             let message = json["message"] as? String
         else { return nil }
-        return SyncError(source: source, name: name, message: message)
+        let calendarId = json["calendar_id"].map { "\($0)" }
+        return SyncError(source: source, calendarId: calendarId, name: name, message: message)
     }
 }
 

Calendarr iOS/Models/CalendarStore.swift

@@ -349,7 +349,8 @@ class CalendarStore {
         do {
             let (fetched, errors) = try await fetchForMode(api: api, start: start, end: end)
             syncErrors = errors
-            mergeIntoCache(fetched, rangeStart: start, rangeEnd: end)
+            mergeIntoCache(fetched, rangeStart: start, rangeEnd: end,
+                           keepKeysInRange: failedCalendarKeys(from: errors))
             refreshFromCache(start: start, end: end)
         } catch {
             // Hard failure – leave `syncErrors` as-is; it reflects the last
@@ -409,7 +410,8 @@ class CalendarStore {
         do {
             let (fetched, errors) = try await fetchForMode(api: api, start: start, end: end)
             syncErrors = errors
-            mergeIntoCache(fetched, rangeStart: start, rangeEnd: end)
+            mergeIntoCache(fetched, rangeStart: start, rangeEnd: end,
+                           keepKeysInRange: failedCalendarKeys(from: errors))
             // Refresh visible range from newly expanded cache
             let (vs, ve) = rangeForCurrentView()
             refreshFromCache(start: vs, end: ve)
@@ -428,10 +430,29 @@ class CalendarStore {
         allCachedEvents = []
     }
 
-    private func mergeIntoCache(_ newEvents: [CalEvent], rangeStart: Date, rangeEnd: Date) {
-        // Remove old events that overlap with the newly fetched range (avoid duplicates)
+    /// Calendar keys (source:id) for calendars that reported a per-source sync
+    /// error. Events from these calendars must NOT be evicted from the cache on
+    /// a partial sync — stale data is better than a completely empty calendar.
+    private func failedCalendarKeys(from errors: [SyncError]) -> Set<String> {
+        var keys = Set<String>()
+        for err in errors {
+            guard let cid = err.calendarId else { continue }
+            keys.insert(Self.calendarKey(source: err.source, calendarId: cid))
+        }
+        return keys
+    }
+
+    private func mergeIntoCache(_ newEvents: [CalEvent], rangeStart: Date, rangeEnd: Date,
+                                 keepKeysInRange: Set<String> = []) {
+        // Remove old events in the fetched range to avoid duplicates — but
+        // PRESERVE events from calendars that had sync errors so that a
+        // transient CalDAV / Google failure doesn't wipe the visible calendar.
         let retained = allCachedEvents.filter { ev in
-            ev.startDate >= rangeEnd || ev.endDate <= rangeStart
+            let outsideRange = ev.startDate >= rangeEnd || ev.endDate <= rangeStart
+            if outsideRange { return true }
+            guard !keepKeysInRange.isEmpty else { return false }
+            let key = Self.calendarKey(source: ev.source, calendarId: ev.calendarId)
+            return keepKeysInRange.contains(key)
         }
         allCachedEvents = retained + newEvents