Watch: give GlucoseStore its own Core Data stack

LoopCore/PersistenceController.swift

@@ -21,13 +21,13 @@ extension PersistenceController {
         return self.init(directoryURL: directoryURL.appendingPathComponent("com.loopkit.LoopKit", isDirectory: true), isReadOnly: isReadOnly)
     }
 
-    public class func controllerInLocalDirectory() -> PersistenceController {
+    public class func controllerInLocalDirectory(named name: String = "com.loopkit.LoopKit") -> PersistenceController {
         guard let directoryURL = try? FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true) else {
             fatalError("Could not access the document directory of the current process")
         }
 
         let isReadOnly = Bundle.main.isAppExtension
 
-        return self.init(directoryURL: directoryURL.appendingPathComponent("com.loopkit.LoopKit"), isReadOnly: isReadOnly)
+        return self.init(directoryURL: directoryURL.appendingPathComponent(name), isReadOnly: isReadOnly)
     }
 }

WatchApp Extension/Managers/LoopDataManager.swift

@@ -111,10 +111,17 @@ class LoopDataManager {
             loopSettings: LoopSettings(),
             scheduleOverride: nil
         )
-
+
+        // Give GlucoseStore its own Core Data stack rather than sharing `cacheStore` with
+        // CarbStore. GlucoseStore drives its context exclusively with the async
+        // `context.perform` API, while CarbStore uses `performAndWait`. Sharing one serial
+        // context between the two mixes those concurrency models and can race, producing a
+        // torn read of a freshly-inserted CachedGlucoseObject (a nil required attribute).
+        // A dedicated context removes that cross-store contention.
+        let glucoseCacheStore = PersistenceController.controllerInLocalDirectory(named: "com.loopkit.LoopKit.Glucose")
         Task {
             glucoseStore = await GlucoseStore(
-                cacheStore: cacheStore,
+                cacheStore: glucoseCacheStore,
                 cacheLength: .hours(4)
             )
         }