Revise entity state and status format and access

src/DurableTask.Core/Entities/ClientEntityHelpers.cs

@@ -70,21 +70,36 @@ public static EventToSend EmitUnlockForOrphanedLock(OrchestrationInstance target
             };
 
             var jmessage = JToken.FromObject(message, Serializer.InternalSerializer);
-
             return new EventToSend(EntityMessageEventNames.ReleaseMessageEventName, jmessage, targetInstance);
         }
 
         /// <summary>
-        /// Extracts the user-defined entity state (as a serialized string) from the scheduler state (also a serialized string).
+        /// Extracts the user-defined entity state from the serialized scheduler state. The result is the serialized state,
+        /// or null if the entity has no state.
         /// </summary>
-        /// <param name="serializedSchedulerState">The state of the scheduler, as a serialized string.</param>
-        /// <param name="entityState">The entity state</param>
-        /// <returns>True if the entity exists, or false otherwise</returns>
-        public static bool TryGetEntityStateFromSerializedSchedulerState(string serializedSchedulerState, out string? entityState)
+        public static string? GetEntityState(string? serializedSchedulerState)
         {
-            var schedulerState = JsonConvert.DeserializeObject<SchedulerState>(serializedSchedulerState, Serializer.InternalSerializerSettings);
-            entityState = schedulerState!.EntityState;
-            return schedulerState.EntityExists;
+            if (serializedSchedulerState == null)
+            {
+                return null;
+            }
+
+            var schedulerState = JsonConvert.DeserializeObject<SchedulerState>(serializedSchedulerState, Serializer.InternalSerializerSettings)!;
+            return schedulerState.EntityState;
+        }
+
+        /// <summary>
+        /// Gets the entity status from the serialized custom status of the orchestration.
+        /// or null if the entity has no state.
+        /// </summary>
+        public static EntityStatus? GetEntityStatus(string? orchestrationCustomStatus)
+        {
+            if (orchestrationCustomStatus == null)
+            {
+                return null;
+            }
+
+            return JsonConvert.DeserializeObject<EntityStatus>(orchestrationCustomStatus, Serializer.InternalSerializerSettings)!;
         }
     }
 }

src/DurableTask.Core/Entities/StateFormat/EntityStatus.cs

@@ -22,10 +22,25 @@ namespace DurableTask.Core.Entities
     [DataContract]
     public class EntityStatus
     {
+        /// <summary>
+        /// The JSON property name for the entityExists property.  
+        /// </summary>
+        const string EntityExistsProperyName = "entityExists";
+
+        /// <summary>
+        /// A fast shortcut for checking whether an entity exists, looking at the serialized json string directly. Used by queries.
+        /// </summary>
+        /// <param name="serializedJson"></param>
+        /// <returns></returns>
+        public static bool TestEntityExists(string serializedJson)
+        {
+            return serializedJson.Contains(EntityExistsProperyName);
+        }
+
         /// <summary>
         /// Whether this entity exists or not.
         /// </summary>
-        [DataMember(Name = "entityExists", EmitDefaultValue = false)]
+        [DataMember(Name = EntityExistsProperyName, EmitDefaultValue = false)]
         public bool EntityExists { get; set; }
 
         /// <summary>

src/DurableTask.Core/Entities/StateFormat/SchedulerState.cs

@@ -24,11 +24,8 @@ namespace DurableTask.Core.Entities
     [DataContract]
     internal class SchedulerState
     {
-        /// <summary>
-        /// Whether this entity exists or not.
-        /// </summary>
-        [DataMember(Name = "exists", EmitDefaultValue = false)]
-        public bool EntityExists { get; set; }
+        [IgnoreDataMember]
+        public bool EntityExists => this.EntityState != null;
 
         /// <summary>
         /// The last serialized entity state.

src/DurableTask.Core/TaskEntityDispatcher.cs

@@ -268,7 +268,6 @@ protected async Task<bool> OnProcessWorkItemAsync(TaskOrchestrationWorkItem work
 
                         // update the entity state based on the result
                         schedulerState.EntityState = result.EntityState;
-                        schedulerState.EntityExists = result.EntityState != null;
 
                         // perform the actions
                         foreach (var action in result.Actions!)