feat(conversation): replace a tool result the assistant message repeats

src/Infrastructure/BotSharp.Core/Conversations/Hooks/ToolResultTrimHook.cs

@@ -4,18 +4,16 @@
 namespace BotSharp.Core.Conversations.Hooks;
 
 /// <summary>
-/// Shortens the tool results an older turn replays into the prompt.
+/// Shortens the tool results an older turn replays into the prompt. It runs where history is
+/// loaded, so the turn that ran a tool still reads its result whole. Only <c>Content</c> is
+/// touched: the call stays intact, and storage keeps the full text.
 /// </summary>
-/// <remarks>
-/// It runs where history is loaded, which is exactly the turn boundary: the messages a turn
-/// produces are appended to the list in memory and never pass through here, so the turn that ran
-/// a tool always reads its result whole. Only <c>Content</c> is touched -- the call itself stays
-/// intact, so a later turn can still tell that the function already ran, and storage keeps the
-/// full text either way.
-/// </remarks>
 public class ToolResultTrimHook : ConversationHookBase
 {
-    /// <summary>The opening of a structured document: a brace or bracket that starts one, not a word in prose.</summary>
+    /// <summary>Stands in for a result the assistant message of the same turn already carries.</summary>
+    private const string RepliedToUser = "[replied to the user]";
+
+    /// <summary>A brace or bracket that opens a value, as opposed to one in a sentence.</summary>
     private static readonly Regex StructuredStart = new(@"[{\[]\s*[""{\[\d-]", RegexOptions.Compiled);
 
     private readonly IServiceProvider _services;
@@ -42,9 +40,8 @@ public override Task OnDialogsLoaded(List<RoleDialogModel> dialogs)
             return base.OnDialogsLoaded(dialogs);
         }
 
-        // A turn is a message id: everything a turn derives carries the id of the message that
-        // started it. The current one is skipped as well, because a function that reloads the
-        // history mid-turn would otherwise be handed a shortened copy of what it just produced.
+        // A turn is a message id. The current one is left alone for a function that reloads the
+        // history mid-turn.
         var currentMessageId = _services.GetRequiredService<IRoutingContext>().MessageId;
         var recentTurns = dialogs
             .Select(x => x.MessageId)
@@ -53,21 +50,39 @@ public override Task OnDialogsLoaded(List<RoleDialogModel> dialogs)
             .TakeLast(Math.Max(setting.KeepTurns, 0))
             .ToHashSet();
 
+        var replies = dialogs
+            .Where(x => x.Role == AgentRole.Assistant && !string.IsNullOrEmpty(x.Content))
+            .Select(x => (x.MessageId, x.Content))
+            .ToHashSet();
+
         var trimmed = 0;
         var saved = 0;
 
         foreach (var dialog in dialogs)
         {
             if (dialog.Role != AgentRole.Function
                 || dialog.MessageId == currentMessageId
-                || recentTurns.Contains(dialog.MessageId)
-                || (dialog.Content?.Length ?? 0) <= setting.MaxLength)
+                || string.IsNullOrEmpty(dialog.Content))
             {
                 continue;
             }
 
             var before = dialog.Content.Length;
-            dialog.Content = Shorten(dialog, setting.MaxLength);
+
+            if (replies.Contains((dialog.MessageId, dialog.Content)))
+            {
+                // Repeating what the assistant message says word for word teaches the model to
+                // answer by echoing tool output. Nothing is lost, so recent turns are no exception.
+                dialog.Content = RepliedToUser;
+            }
+            else if (!recentTurns.Contains(dialog.MessageId) && before > setting.MaxLength)
+            {
+                dialog.Content = Shorten(dialog, setting.MaxLength);
+            }
+            else
+            {
+                continue;
+            }
 
             trimmed++;
             saved += before - dialog.Content.Length;
@@ -76,34 +91,25 @@ public override Task OnDialogsLoaded(List<RoleDialogModel> dialogs)
         if (trimmed > 0)
         {
             _logger.LogInformation(
-                "[ToolResultTrim] {Count} tool result(s) older than {KeepTurns} turn(s) shortened, {Saved} characters kept out of the prompt.",
-                trimmed, setting.KeepTurns, saved);
+                "[ToolResultTrim] {Count} tool result(s) shortened, {Saved} characters kept out of the prompt.",
+                trimmed, saved);
         }
 
         return base.OnDialogsLoaded(dialogs);
     }
 
     /// <summary>
-    /// Keeps the head of a rendered result, whose useful part comes first, and replaces a
-    /// structured one outright: half a JSON document is not something a model can read, and it
-    /// cannot tell that the half it got is not the whole.
+    /// Cuts wherever comes first, a structured value or the length cap. Half a document is
+    /// something a model can neither read nor tell is incomplete, so one is replaced outright,
+    /// while the sentence that introduced it is worth keeping.
     /// </summary>
-    /// <remarks>
-    /// The cut goes wherever comes first: where a structured value begins, or the length cap. A
-    /// tool is free to answer with a sentence and then a document -- an MCP server returning
-    /// several text blocks does exactly that -- and cutting inside the document would leave a
-    /// model something it cannot read and cannot tell is incomplete, while cutting in front of it
-    /// keeps the sentence that introduced it. A lone brace in prose is not a document: what is
-    /// looked for is a brace or bracket that opens a value.
-    /// </remarks>
     private static string Shorten(RoleDialogModel dialog, int maxLength)
     {
         var content = dialog.Content;
         var structure = StructuredStart.Match(content);
         var cut = structure.Success ? Math.Min(structure.Index, maxLength) : maxLength;
 
-        // The call itself sits in the message right before this one, so the note does not name it
-        // again -- what a later turn cannot work out on its own is that something was dropped.
+        // The call is named in the message right before this one, so the note does not repeat it.
         if (cut == 0)
         {
             return $"[{content.Length} chars omitted; call again for detail]";

tests/BotSharp.Core.UnitTests/Conversations/ToolResultTrimHookTests.cs

@@ -207,6 +207,72 @@ public async Task Leaves_a_short_result_alone()
         Assert.Equal(400, dialogs[0].Content.Length);
     }
 
+    [Fact]
+    public async Task Stands_in_for_a_result_the_assistant_message_repeats()
+    {
+        // A function that writes the user-facing reply itself has its text stored twice. Short
+        // enough to pass the length cap, and shown to the model as a tool result echoed word for
+        // word by the assistant -- which is what the model then learns to do.
+        const string reply = "Are you creating a duplicate work order or not?";
+        var dialogs = new List<RoleDialogModel>
+        {
+            Tool(OldTurn, reply, function: "check_prerequisites"),
+            new(AgentRole.Assistant, reply) { MessageId = OldTurn }
+        };
+
+        await BuildHook(Settings(keepTurns: 0), CurrentTurn).OnDialogsLoaded(dialogs);
+
+        Assert.Equal("[replied to the user]", dialogs[0].Content);
+        Assert.Equal("check_prerequisites", dialogs[0].FunctionName);
+        Assert.Equal(reply, dialogs[1].Content);
+    }
+
+    [Fact]
+    public async Task Leaves_a_result_the_assistant_only_paraphrased()
+    {
+        var dialogs = new List<RoleDialogModel>
+        {
+            Tool(OldTurn, "Got location id 750229, resident id 1673151, continue current process."),
+            new(AgentRole.Assistant, "Got it. Can you tell me about the issue?") { MessageId = OldTurn }
+        };
+
+        await BuildHook(Settings(keepTurns: 0), CurrentTurn).OnDialogsLoaded(dialogs);
+
+        Assert.StartsWith("Got location id 750229", dialogs[0].Content);
+    }
+
+    [Fact]
+    public async Task Stands_in_even_for_a_turn_that_keeps_its_results()
+    {
+        // Shortening spares the recent turns because their detail may still be wanted. A repeat
+        // has no detail to spare: the assistant message beside it says the same thing.
+        const string reply = "Are you ready for some questions?";
+        var dialogs = new List<RoleDialogModel>
+        {
+            Tool(RecentTurn, reply),
+            new(AgentRole.Assistant, reply) { MessageId = RecentTurn }
+        };
+
+        await BuildHook(Settings(keepTurns: 2), CurrentTurn).OnDialogsLoaded(dialogs);
+
+        Assert.Equal("[replied to the user]", dialogs[0].Content);
+    }
+
+    [Fact]
+    public async Task Does_not_match_the_same_text_from_another_turn()
+    {
+        const string reply = "Are you creating a duplicate work order or not?";
+        var dialogs = new List<RoleDialogModel>
+        {
+            Tool(OldTurn, reply),
+            new(AgentRole.Assistant, reply) { MessageId = MiddleTurn }
+        };
+
+        await BuildHook(Settings(keepTurns: 0), CurrentTurn).OnDialogsLoaded(dialogs);
+
+        Assert.Equal(reply, dialogs[0].Content);
+    }
+
     [Fact]
     public async Task Does_nothing_at_all_when_switched_off()
     {