fix: prevent repeated off-hours handoff notices

internal/services/conversation_human_dispatch_service_test.go

@@ -47,6 +47,32 @@ func TestConversationHumanDispatchAIHandoffOffHoursKeepsAIServingAndSendsNotice(
 	}
 }
 
+func TestConversationHumanDispatchAIHandoffOffHoursDoesNotDuplicateNotice(t *testing.T) {
+	db := setupConversationHumanDispatchTestDB(t)
+	aiAgent := createHumanDispatchAIAgent(t, db, enums.IMConversationServiceModeAIFirst, "1")
+	conversation := createHumanDispatchConversation(t, db, aiAgent.ID, enums.IMConversationStatusAIServing)
+
+	for i := 0; i < 3; i++ {
+		result, err := services.ConversationHumanDispatchService.HandoffByAI(conversation.ID, aiAgent, "用户要求转人工")
+		if err != nil {
+			t.Fatalf("HandoffByAI() round %d error = %v", i+1, err)
+		}
+		if result == nil || result.Decision != services.HandoffDecisionOffHours {
+			t.Fatalf("expected off_hours decision on round %d, got %+v", i+1, result)
+		}
+	}
+
+	var count int64
+	if err := db.Model(&models.Message{}).
+		Where("conversation_id = ? AND sender_type = ? AND content = ?", conversation.ID, enums.IMSenderTypeAI, services.HandoffOffHoursMessage).
+		Count(&count).Error; err != nil {
+		t.Fatalf("count off-hours messages error = %v", err)
+	}
+	if count != 1 {
+		t.Fatalf("expected one off-hours notice, got %d", count)
+	}
+}
+
 func TestConversationHumanDispatchAIHandoffAssignsAvailableAgent(t *testing.T) {
 	db := setupConversationHumanDispatchTestDB(t)
 	aiAgent := createHumanDispatchAIAgent(t, db, enums.IMConversationServiceModeAIFirst, "1")