diff --git a/pkg/agent/context.go b/pkg/agent/context.go
index 1ccf32611..9d87938b5 100644
--- a/pkg/agent/context.go
+++ b/pkg/agent/context.go
@@ -876,7 +876,7 @@ func messageHistoryAnnotation(msg providers.Message) string {
 	if len(parts) == 0 {
 		return ""
 	}
-	return fmt.Sprintf("[%s] ", strings.Join(parts, ", "))
+	return fmt.Sprintf("[%s] ", strings.Join(parts, "; "))
 }
 
 func messageSenderAnnotation(sender *providers.MessageSender) string {
diff --git a/pkg/agent/context_test.go b/pkg/agent/context_test.go
index 08cec97b8..7337e8b4a 100644
--- a/pkg/agent/context_test.go
+++ b/pkg/agent/context_test.go
@@ -226,7 +226,7 @@ func TestMessageHistoryAnnotation_IncludesSenderAndThreading(t *testing.T) {
 		},
 	}
 
-	if got := messageHistoryAnnotation(msg); got != "[from:Alice Example (@alice), msgs:#m1, reply_to:#p0] " {
+	if got := messageHistoryAnnotation(msg); got != "[from:Alice Example (@alice); msgs:#m1, reply_to:#p0] " {
 		t.Fatalf("messageHistoryAnnotation() = %q", got)
 	}
 }