feat(twilio): keep a reply the caller cut off as the part they heard

src/Plugins/BotSharp.Plugin.Twilio/Models/AgentTurnCallbacks.cs

@@ -27,4 +27,10 @@ public class AgentTurnCallbacks
     /// and the tool may take a while before anything else is said
     /// </summary>
     public Func<Task>? OnStreamEndedWithToolCall { get; init; }
+
+    /// <summary>
+    /// The last say over what the conversation history keeps of the reply: called with the reply the agent wrote,
+    /// returns what is stored in its place. Lets a flow record a reply the caller cut off as the part they heard.
+    /// </summary>
+    public Func<string, string>? RewriteReply { get; init; }
 }

src/Plugins/BotSharp.Plugin.Twilio/Services/ConversationRelaySession.cs

@@ -51,6 +51,7 @@ public class ConversationRelaySession
     private bool _utteranceOpen;
     private bool _streamedThisTurn;
     private bool _dropStream;
+    private bool _cutInMidReply;
 
     // The current turn's reply is in; the response watchdog says nothing more once it is set
     private bool _turnReplied;
@@ -235,6 +236,7 @@ private async Task HandleMessageAsync(string json)
                     if (_isProcessing && _streamedThisTurn)
                     {
                         _dropStream = true;
+                        _cutInMidReply = true;
                     }
                 }
                 var interruptedAfter = GetString(root, "durationUntilInterruptMs");
@@ -316,6 +318,7 @@ private async Task ProcessPendingAsync()
                 _utteranceOpen = false;
                 _streamedThisTurn = false;
                 _dropStream = false;
+                _cutInMidReply = false;
                 _turnReplied = false;
                 _turnStartedUtc = DateTime.UtcNow;
             }
@@ -333,7 +336,8 @@ private async Task ProcessPendingAsync()
                 OnStreamStarted = stream ? CloseUtteranceAsync : null,
                 // A line said before a slow tool ("Okay, that's everything I need") is spoken now, and the watchdog
                 // counts the silence after it instead of waiting for the next response to close it
-                OnStreamEndedWithToolCall = stream ? CloseUtteranceAsync : null
+                OnStreamEndedWithToolCall = stream ? CloseUtteranceAsync : null,
+                RewriteReply = stream ? MarkWhatTheCallerCutOff : null
             };
 
             AssistantMessage? reply;
@@ -587,6 +591,40 @@ await SendIfAsync(() =>
         }, new { type = "text", token = string.Empty, last = true });
     }
 
+    /// <summary>
+    /// What the conversation history keeps of a reply the caller cut in on: the part that went out, and after it a
+    /// mark naming the rest, so the next turn knows the caller never heard it. Every other reply is kept as it is.
+    /// </summary>
+    /// <remarks>
+    /// Only a reply cut off while it was still being streamed can be marked: once the whole reply is out, Twilio
+    /// holds the text it has yet to speak and a cut-in there leaves nothing of ours to go by.
+    /// </remarks>
+    private string MarkWhatTheCallerCutOff(string content)
+    {
+        var final = content?.Trim() ?? string.Empty;
+        string sent;
+        lock (_sync)
+        {
+            if (!_cutInMidReply || final.Length == 0)
+            {
+                return content;
+            }
+            sent = (_utteranceOpen ? _streamSegment.ToString() : _lastStreamSegment).Trim();
+        }
+
+        // The reply is not what was streamed (text set by a tool, or a reply rewritten after the model wrote it),
+        // so where the caller cut in is not known
+        if (sent.Length == 0 || !final.StartsWith(sent, StringComparison.Ordinal))
+        {
+            return content;
+        }
+
+        var unheard = final.Substring(sent.Length).Trim();
+        return unheard.Length == 0
+            ? content
+            : $"{sent} [the caller cut in here; they did not hear: \"{unheard}\"]";
+    }
+
     /// <summary>
     /// The part of the final reply that was not streamed. Normally nothing; the whole reply when it is not
     /// what the model streamed last, e.g. text set by a tool, or a reply rewritten after the model wrote it.

src/Plugins/BotSharp.Plugin.Twilio/Services/TwilioConversationProcessor.cs

@@ -99,11 +99,14 @@ await conv.SendMessage(message.AgentId,
             replyMessage: await BuildPostbackMessageModel(conv, message),
             async msg =>
             {
+                // What the caller is told, which a rewrite below must not change
+                var spoken = msg.Content;
+                RewriteForHistory(msg, callbacks);
                 reply = new AssistantMessage()
                 {
                     ConversationEnd = msg.Instruction?.ConversationEnd ?? false,
                     HumanIntervationNeeded = string.Equals("human_intervention_needed", msg.FunctionName),
-                    Content = msg.Content,
+                    Content = spoken,
                     MessageId = msg.MessageId
                 };
             }
@@ -112,6 +115,31 @@ await conv.SendMessage(message.AgentId,
         return reply;
     }
 
+    /// <summary>
+    /// Lets the flow change what the history keeps of the reply. The dialog is appended after this callback runs,
+    /// so the message changed here is the one that is stored.
+    /// </summary>
+    private static void RewriteForHistory(RoleDialogModel msg, AgentTurnCallbacks? callbacks)
+    {
+        if (callbacks?.RewriteReply == null || string.IsNullOrEmpty(msg.Content))
+        {
+            return;
+        }
+
+        var stored = callbacks.RewriteReply(msg.Content);
+        if (string.IsNullOrEmpty(stored) || stored == msg.Content)
+        {
+            return;
+        }
+
+        // Kept in step only where it is the reply itself; a rich message the model refined is left alone
+        if (msg.RichContent?.Message != null && msg.RichContent.Message.Text == msg.Content)
+        {
+            msg.RichContent.Message.Text = stored;
+        }
+        msg.Content = stored;
+    }
+
     private static async Task<PostbackMessageModel?> BuildPostbackMessageModel(
         IConversationService conv, CallerMessage message)
     {