Prevent duplication of user prompts / chat history in ChatSession.

The way ChatSession.ChatAsync was using the provided methods
from a IHistoryTransform interface implementation created unexpected
duplication of the chat history messages. It also prevented loading
previous history into the current session.

LLama/ChatSession.cs

@@ -95,11 +95,11 @@ namespace LLama
                 Directory.CreateDirectory(path);
             }
             _executor.Context.SaveState(Path.Combine(path, _modelStateFilename));
-            if(Executor is StatelessExecutor)
+            if (Executor is StatelessExecutor)
             {
 
             }
-            else if(Executor is StatefulExecutorBase statefulExecutor)
+            else if (Executor is StatefulExecutorBase statefulExecutor)
             {
                 statefulExecutor.SaveState(Path.Combine(path, _executorStateFilename));
             }
@@ -135,30 +135,54 @@ namespace LLama
         }
 
         /// <summary>
-        /// Get the response from the LLama model. Note that prompt could not only be the preset words, 
-        /// but also the question you want to ask.
+        /// Generates a response for a given user prompt and manages history state for the user.
+        /// This will always pass the whole history to the model. Don't pass a whole history
+        /// to this method as the user prompt will be appended to the history of the current session.
+        /// If more control is needed, use the other overload of this method that accepts a ChatHistory object.
         /// </summary>
         /// <param name="prompt"></param>
         /// <param name="inferenceParams"></param>
         /// <param name="cancellationToken"></param>
-        /// <returns></returns>
+        /// <returns>Returns generated tokens of the assistant message.</returns>
         public async IAsyncEnumerable<string> ChatAsync(string prompt, IInferenceParams? inferenceParams = null, [EnumeratorCancellation] CancellationToken cancellationToken = default)
         {
-            foreach(var inputTransform in InputTransformPipeline)
+            foreach (var inputTransform in InputTransformPipeline)
                 prompt = inputTransform.Transform(prompt);
-            
-            History.Messages.AddRange(HistoryTransform.TextToHistory(AuthorRole.User, prompt).Messages);
+
+            History.Messages.Add(new ChatHistory.Message(AuthorRole.User, prompt));
+
+            string internalPrompt = HistoryTransform.HistoryToText(History);
+
             StringBuilder sb = new();
-            await foreach (var result in ChatAsyncInternal(prompt, inferenceParams, cancellationToken))
+
+            await foreach (var result in ChatAsyncInternal(internalPrompt, inferenceParams, cancellationToken))
             {
                 yield return result;
                 sb.Append(result);
             }
-            History.Messages.AddRange(HistoryTransform.TextToHistory(AuthorRole.Assistant, sb.ToString()).Messages);
+
+            string assistantMessage = sb.ToString();
+
+            // Remove end tokens from the assistant message
+            // if defined in inferenceParams.AntiPrompts.
+            // We only want the response that was generated and not tokens
+            // that are delimiting the beginning or end of the response.
+            if (inferenceParams?.AntiPrompts != null)
+            {
+                foreach (var stopToken in inferenceParams.AntiPrompts)
+                {
+                    assistantMessage = assistantMessage.Replace(stopToken, "");
+                }
+            }
+
+            History.Messages.Add(new ChatHistory.Message(AuthorRole.Assistant, assistantMessage));
         }
 
         /// <summary>
-        /// Get the response from the LLama model with chat histories.
+        /// Generates a response for a given chat history. This method does not manage history state for the user.
+        /// If you want to e.g. truncate the history of a session to fit into the model's context window,
+        /// use this method and pass the truncated history to it. If you don't need this control, use the other
+        /// overload of this method that accepts a user prompt instead.
         /// </summary>
         /// <param name="history"></param>
         /// <param name="inferenceParams"></param>
@@ -167,14 +191,14 @@ namespace LLama
         public async IAsyncEnumerable<string> ChatAsync(ChatHistory history, IInferenceParams? inferenceParams = null, [EnumeratorCancellation] CancellationToken cancellationToken = default)
         {
             var prompt = HistoryTransform.HistoryToText(history);
-            History.Messages.AddRange(HistoryTransform.TextToHistory(AuthorRole.User, prompt).Messages);
+
             StringBuilder sb = new();
+
             await foreach (var result in ChatAsyncInternal(prompt, inferenceParams, cancellationToken))
             {
                 yield return result;
                 sb.Append(result);
             }
-            History.Messages.AddRange(HistoryTransform.TextToHistory(AuthorRole.Assistant, sb.ToString()).Messages);
         }
 
         private async IAsyncEnumerable<string> ChatAsyncInternal(string prompt, IInferenceParams? inferenceParams = null, [EnumeratorCancellation] CancellationToken cancellationToken = default)