Add message limit to chat history management

Updated `ChatService` to enforce a message limit based on the new `MessageLimit` property in `AppSettings`. Excess messages are removed before updating the cache to optimize performance. Adjusted `appsettings.json` to reflect the new configuration, changing `MaxInputTokens` from 16385 to 16384 and adding `MessageLimit` with a default value of 20.

SqlDatabaseVectorSearch/Services/ChatService.cs

@@ -156,7 +156,14 @@ public class ChatService(IChatCompletionService chatCompletionService, Tokenizer
     }
 
     private async Task UpdateCacheAsync(Guid conversationId, ChatHistory chat, CancellationToken cancellationToken)
-        => await cache.SetAsync(conversationId.ToString(), chat, cancellationToken: cancellationToken);
+    {
+        if (chat.Count > appSettings.MessageLimit)
+        {
+            chat.RemoveRange(0, chat.Count - appSettings.MessageLimit);
+        }
+
+        await cache.SetAsync(conversationId.ToString(), chat, cancellationToken: cancellationToken);
+    }
 
     private async Task<ChatHistory> GetChatHistoryAsync(Guid conversationId, CancellationToken cancellationToken)
     {

SqlDatabaseVectorSearch/Settings/AppSettings.cs

@@ -15,4 +15,6 @@ public class AppSettings
     public int MaxOutputTokens { get; init; } = 800;
 
     public TimeSpan MessageExpiration { get; init; }
+
+    public int MessageLimit { get; set; } = 20;
 }

SqlDatabaseVectorSearch/appsettings.json

@@ -24,9 +24,10 @@
         "MaxTokensPerParagraph": 1000,
         "OverlapTokens": 100,
         "MaxRelevantChunks": 10,
-        "MaxInputTokens": 16385,
+        "MaxInputTokens": 16384,
         "MaxOutputTokens": 800,
-        "MessageExpiration": "00:05:00"
+        "MessageExpiration": "00:05:00",
+        "MessageLimit": 20
     },
     "Logging": {
         "LogLevel": {