Fix timeline position sync not working due to LazilyDecoding cache not being invalidated upon remote change

Tusker/CoreData/MastodonCachePersistentStore.swift

@@ -545,6 +545,8 @@ class MastodonCachePersistentStore: NSPersistentCloudKitContainer {
                             guard let timelinePosition = try? self.viewContext.existingObject(with: id) as? TimelinePosition else {
                                 continue
                             }
+                            // the kvo observer that clears the LazilyDecoding cache doesn't always fire on remote changes, so do it manually
+                            timelinePosition.changedRemotely()
                             NotificationCenter.default.post(name: .timelinePositionChanged, object: timelinePosition)
                         }
                         if changedAccountPrefs {

Tusker/CoreData/TimelinePosition.swift

@@ -41,6 +41,10 @@ public final class TimelinePosition: NSManagedObject {
         self.createdAt = Date()
     }
     
+    func changedRemotely() {
+        _statusIDs.removeCachedValue()
+    }
+    
 }
 
 // blergh, this is the simplest way of getting the Timeline into a format that A) CoreData can handle and B) is usable in the predicate

Tusker/LazilyDecoding.swift

@@ -18,6 +18,7 @@ public struct LazilyDecoding<Enclosing: NSObject, Value: Codable> {
     private let fallback: Value
     private var value: Value?
     private var observation: NSKeyValueObservation?
+    private var skipClearingOnNextUpdate = false
     
     init(from keyPath: ReferenceWritableKeyPath<Enclosing, Data?>, fallback: Value) {
         self.keyPath = keyPath
@@ -37,13 +38,16 @@ public struct LazilyDecoding<Enclosing: NSObject, Value: Codable> {
             } else {
                 guard let data = instance[keyPath: wrapper.keyPath] else { return wrapper.fallback }
                 do {
-                    let value = try decoder.decode(Box<Value>.self, from: data)
+                    let value = try decoder.decode(Box.self, from: data)
                     wrapper.value = value.value
                     wrapper.observation = instance.observe(wrapper.keyPath, changeHandler: { instance, _ in
-                        var updated = instance[keyPath: storageKeyPath]
+                        var wrapper = instance[keyPath: storageKeyPath]
-                        updated.value = nil
+                        if wrapper.skipClearingOnNextUpdate {
-                        updated.observation = nil
+                            wrapper.skipClearingOnNextUpdate = false
-                        instance[keyPath: storageKeyPath] = updated
+                        } else {
+                            wrapper.removeCachedValue()
+                        }
+                        instance[keyPath: storageKeyPath] = wrapper
                     })
                     instance[keyPath: storageKeyPath] = wrapper
                     return value.value
@@ -55,12 +59,18 @@ public struct LazilyDecoding<Enclosing: NSObject, Value: Codable> {
         set {
             var wrapper = instance[keyPath: storageKeyPath]
             wrapper.value = newValue
+            wrapper.skipClearingOnNextUpdate = true
             instance[keyPath: storageKeyPath] = wrapper
             let newData = try! encoder.encode(Box(value: newValue))
             instance[keyPath: wrapper.keyPath] = newData
         }
     }
     
+    mutating func removeCachedValue() {
+        value = nil
+        observation = nil
+    }
+    
 }
 
 extension LazilyDecoding {
@@ -72,7 +82,7 @@ extension LazilyDecoding {
 extension LazilyDecoding {
     // PropertyListEncoder only allows top-level types to be dicts or arrays, which breaks encoding nil-able values.
     // Wrapping everything in a Box ensures that it's always a dict.
-    private struct Box<T: Codable>: Codable {
+    struct Box: Codable {
-        let value: T
+        let value: Value
     }
 }

Tusker/Screens/Timeline/TimelineViewController.swift

@@ -589,6 +589,7 @@ class TimelineViewController: UIViewController, TimelineLikeCollectionViewContro
         guard timelinePosition.centerStatusID != centerVisibleStatusID else {
             return false
         }
+        stateRestorationLogger.info("Potential restore with centerStatusID: \(timelinePosition.centerStatusID ?? "<none>")")
         if !alwaysPrompt {
             Task {
                 _ = await restoreState()