Cleanups

Author: javiercn

src/Components/Components/src/ComponentSubscriptionKey.cs

@@ -5,7 +5,8 @@
 
 namespace Microsoft.AspNetCore.Components.Infrastructure;
 
-internal struct ComponentSubscriptionKey(ComponentState subscriber, string propertyName) : IEquatable<ComponentSubscriptionKey>
+// TODO: Add debugger display to show the component state component type and property name.
+internal readonly struct ComponentSubscriptionKey(ComponentState subscriber, string propertyName) : IEquatable<ComponentSubscriptionKey>
 {
     public ComponentState Subscriber { get; } = subscriber;
 

src/Components/Components/src/PersistentState/ComponentStatePersistenceManager.cs

@@ -73,23 +73,22 @@ public async Task RestoreStateAsync(IPersistentComponentStateStore store, Restor
 
         if (_stateIsInitialized)
         {
+            if (context != RestoreContext.ValueUpdate)
+            {
+                throw new InvalidOperationException("State already initialized.");
+            }
             State.UpdateExistingState(data, context);
+            foreach (var registration in _registeredRestoringCallbacks)
+            {
+                registration.Callback();
+            }
         }
         else
         {
             State.InitializeExistingState(data, context);
             _servicesRegistry?.RegisterForPersistence(State);
             _stateIsInitialized = true;
         }
-
-        if (context == RestoreContext.ValueUpdate)
-        {
-            foreach (var registration in _registeredRestoringCallbacks)
-            {
-                registration.Callback();
-            }
-            return;
-        }
     }
 
     /// <summary>