добавила реализацию для первого хранилища

SushiBarListImplements/DataListSingleton.cs

@@ -10,6 +10,7 @@ namespace SushiBarListImplement
         public List<Sushi> Sushis { get; set; }
         public List<Client> Clients { get; set; }
         public List<Implementer> Implementers { get; set; }
+        public List<MessageInfo> Messages { get; set; }
         private DataListSingleton()
         {
             Components = new List<Component>();
@@ -17,6 +18,7 @@ namespace SushiBarListImplement
             Sushis = new List<Sushi>();
             Clients = new List<Client>();
             Implementers = new List<Implementer>();
+            Messages = new List<MessageInfo>();
         }
         public static DataListSingleton GetInstance()
         {

SushiBarListImplements/Implements/MessageInfoStorage.cs

@@ -0,0 +1,71 @@
+using SushiBarContracts.BindingModel;
+using SushiBarContracts.SearchModel;
+using SushiBarContracts.StoragesContracts;
+using SushiBarContracts.ViewModels;
+using SushiBarListImplement;
+using SushiBarListImplements.Models;
+
+namespace SushiBarListImplements.Implements
+{
+    public class MessageInfoStorage : IMessageInfoStorage
+    {
+        private readonly DataListSingleton source;
+
+        public MessageInfoStorage(DataListSingleton source)
+        {
+            this.source = source;
+        }
+
+        public MessageInfoViewModel? GetElement(MessageInfoSearchModel model)
+        {
+            if(string.IsNullOrEmpty(model.MessageId) || !model.ClientId.HasValue)
+            {
+                return null;
+            }
+
+            foreach (var message in source.Messages)
+            {
+                if (message.MessageId.Equals(model.MessageId))
+                {
+                    return message.GetViewModel;
+                }
+            }
+
+            return null;
+        }
+
+        public List<MessageInfoViewModel> GetFilteredList(MessageInfoSearchModel model)
+        {
+            var list = new List<MessageInfoViewModel>();
+            foreach (var msg in source.Messages)
+            {
+                if (msg.ClientId.HasValue && model.ClientId == msg.ClientId)
+                {
+                    list.Add(msg.GetViewModel);
+                }
+            }
+            return list;
+        }
+
+        public List<MessageInfoViewModel> GetFullList()
+        {
+            var list = new List<MessageInfoViewModel>();
+            foreach (var msg in source.Messages)
+            {
+                list.Add(msg.GetViewModel);
+            }
+            return list;
+        }
+
+        public MessageInfoViewModel? Insert(MessageInfoBindingModel model)
+        {
+            var newMessage = MessageInfo.Create(model);
+            if (newMessage == null)
+            {
+                return null;
+            }
+            source.Messages.Add(newMessage);
+            return newMessage.GetViewModel;
+        }
+    }
+}

SushiBarListImplements/Models/MessageInfo.cs

@@ -0,0 +1,45 @@
+using SushiBarContracts.BindingModel;
+using SushiBarContracts.ViewModels;
+using SushiBarDataModels;
+
+namespace SushiBarListImplements.Models
+{
+    public class MessageInfo : IMessageInfoModel
+    {
+        public string MessageId { get; set; } = string.Empty;
+
+        public int? ClientId { get; set; }
+
+        public string SenderName { get; set; } = string.Empty;
+
+        public DateTime DateDelivery { get; set; } = DateTime.Now;
+
+        public string Subject { get; set; } = string.Empty;
+
+        public string Body { get; set; } = string.Empty;
+
+        public static MessageInfo? Create(MessageInfoBindingModel? model)
+        {
+            if (model == null) return null;
+            return new MessageInfo
+            {
+                MessageId = model.MessageId,
+                ClientId = model.ClientId,
+                SenderName = model.SenderName,
+                DateDelivery = model.DateDelivery,
+                Subject = model.Subject,
+                Body = model.Body,
+            };
+        }
+
+        public MessageInfoViewModel GetViewModel => new()
+        {
+            MessageId = MessageId,
+            ClientId = ClientId,
+            SenderName = SenderName,
+            DateDelivery = DateDelivery,
+            Subject = Subject,
+            Body = Body,
+        }; 
+    }
+}