add assistant to canvas chat history (#3201)

### What problem does this PR solve?

#3185

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/apps/api_app.py

@@ -261,6 +261,7 @@ def completion():
                                                        ensure_ascii=False) + "\n\n"
 
                         canvas.messages.append({"role": "assistant", "content": final_ans["content"], "id": message_id})
+                        canvas.history.append(("assistant", final_ans["content"]))
                         if final_ans.get("reference"):
                             canvas.reference.append(final_ans["reference"])
                         cvs.dsl = json.loads(str(canvas))

api/apps/canvas_app.py

@@ -133,6 +133,7 @@ def run():
                     yield "data:" + json.dumps({"retcode": 0, "retmsg": "", "data": ans}, ensure_ascii=False) + "\n\n"
 
                 canvas.messages.append({"role": "assistant", "content": final_ans["content"], "id": message_id})
+                canvas.history.append(("assistant", final_ans["content"]))
                 if final_ans.get("reference"):
                     canvas.reference.append(final_ans["reference"])
                 cvs.dsl = json.loads(str(canvas))

api/db/services/dialog_service.py

@@ -164,7 +164,7 @@ def chat(dialog, messages, stream=True, **kwargs):
     embd_mdl = LLMBundle(dialog.tenant_id, LLMType.EMBEDDING, embd_nms[0])
     if not embd_mdl:
         raise LookupError("Embedding model(%s) not found" % embd_nms[0])
-    
+
     if llm_id2llm_type(dialog.llm_id) == "image2text":
         chat_mdl = LLMBundle(dialog.tenant_id, LLMType.IMAGE2TEXT, dialog.llm_id)
     else: