From f533990e86e182b3d8cb0aa80cddb7a5ae8da5b1 Mon Sep 17 00:00:00 2001
From: PratikDhanave <i.pratikdhanave@gmail.com>
Date: Fri, 24 Jul 2026 09:30:02 +0530
Subject: [PATCH] Join Response.String() messages with a newline like .NET
 ConcatText

Response.String() flattened every message's text into one builder with no
separator, so a multi-message assistant turn returned "fooBar" where .NET
AgentResponse.Text (backed by ChatMessage list ConcatText) returns "foo\nBar".
Join each non-empty per-message text with a newline, skipping empty messages,
matching .NET semantics. This also aligns the agent-as-tool result returned by
agenttool's FuncTool, which surfaces resp.String().
---
 agent/response.go      | 14 ++++++++++----
 agent/response_test.go | 41 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 4 deletions(-)

diff --git a/agent/response.go b/agent/response.go
index 6bd8aa4b..a05f6621 100644
--- a/agent/response.go
+++ b/agent/response.go
@@ -69,11 +69,17 @@ func (resp *Response) String() string {
 	}
 	var sb strings.Builder
 	for _, msg := range resp.Messages {
-		for _, c := range msg.Contents {
-			if textContent, ok := c.(*message.TextContent); ok {
-				sb.WriteString(textContent.Text)
-			}
+		// msg.String() equals message.Contents.Text(), the per-message join.
+		// Add a newline separator between each non-empty message, matching
+		// .NET's ChatMessage list ConcatText / AgentResponse.Text.
+		t := msg.String()
+		if t == "" {
+			continue
+		}
+		if sb.Len() > 0 {
+			sb.WriteByte('\n')
 		}
+		sb.WriteString(t)
 	}
 	return sb.String()
 }
diff --git a/agent/response_test.go b/agent/response_test.go
index 6ed913fd..e0475aa0 100644
--- a/agent/response_test.go
+++ b/agent/response_test.go
@@ -788,3 +788,44 @@ func TestResponse_ToUpdates_WithAdditionalPropertiesOnlyProducesSingleUpdate(t *
 		t.Errorf("expected key value, got %v", updates[0].AdditionalProperties["key"])
 	}
 }
+
+func TestResponse_String(t *testing.T) {
+	msg := func(texts ...string) *message.Message {
+		var contents message.Contents
+		for _, text := range texts {
+			contents = append(contents, &message.TextContent{Text: text})
+		}
+		return &message.Message{Role: message.RoleAssistant, Contents: contents}
+	}
+
+	tests := []struct {
+		name     string
+		messages []*message.Message
+		want     string
+	}{
+		{
+			name:     "two messages joined with newline",
+			messages: []*message.Message{msg("foo"), msg("Bar")},
+			want:     "foo\nBar",
+		},
+		{
+			name:     "empty middle message skipped without double newline",
+			messages: []*message.Message{msg("foo"), msg(""), msg("Bar")},
+			want:     "foo\nBar",
+		},
+		{
+			name:     "multiple text contents stay glued within a message",
+			messages: []*message.Message{msg("a", "b")},
+			want:     "ab",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			resp := &agent.Response{Messages: tt.messages}
+			if got := resp.String(); got != tt.want {
+				t.Errorf("String() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}