diff --git a/agent/canvas.py b/agent/canvas.py
index 8de3d4bfcc..fde3e8db82 100644
--- a/agent/canvas.py
+++ b/agent/canvas.py
@@ -329,6 +329,11 @@ class Canvas(Graph):
         self.dsl["memory"] = self.memory
         return super().__str__()
 
+    def clear_history(self):
+        self.history = []
+        if isinstance(self.globals.get("sys.history"), list):
+            self.globals["sys.history"] = []
+
     def reset(self, mem=False):
         super().reset()
         if not mem:
diff --git a/agent/component/categorize.py b/agent/component/categorize.py
index 3bc48e22db..4b5c39631c 100644
--- a/agent/component/categorize.py
+++ b/agent/component/categorize.py
@@ -40,7 +40,8 @@ class CategorizeParam(LLMParam):
         self.update_prompt()
 
     def check(self):
-        self.check_positive_integer(self.message_history_window_size, "[Categorize] Message window size > 0")
+        if not isinstance(self.message_history_window_size, int) or self.message_history_window_size < 0:
+            raise ValueError("[Categorize] Message window size cannot be negative")
         self.check_empty(self.category_description, "[Categorize] Category examples")
         for k, v in self.category_description.items():
             if not k:
diff --git a/api/apps/restful_apis/agent_api.py b/api/apps/restful_apis/agent_api.py
index 69ad700048..aff36cc621 100644
--- a/api/apps/restful_apis/agent_api.py
+++ b/api/apps/restful_apis/agent_api.py
@@ -1447,6 +1447,7 @@ async def agent_chat_completion(tenant_id, agent_id=None):
             from agent.canvas import Canvas
 
             canvas = Canvas(dsl_str, str(tenant_id), canvas_id=agent_id, custom_header=custom_header)
+            canvas.clear_history()
         except Exception as exc:
             return server_error_response(exc)
         turn_id = get_uuid()