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)

agent/canvas.py

 #  See the License for the specific language governing permissions and
 #  limitations under the License.
 #
-import importlib
 import json
 import traceback
 from abc import ABC
 from copy import deepcopy
 from functools import partial
-
-import pandas as pd
-
 from agent.component import component_class
 from agent.component.base import ComponentBase
 from agent.settings import flow_logger, DEBUG
     def get_history(self, window_size):
         convs = []
         for role, obj in self.history[window_size * -1:]:
-            convs.append({"role": role, "content": (obj if role == "user" else
-                    '\n'.join([str(s) for s in pd.DataFrame(obj)['content']]))})
+            if isinstance(obj, list) and obj and all([isinstance(o, dict) for o in obj]):
+                convs.append({"role": role, "content": '\n'.join([str(s.get("content", "")) for s in obj])})
+            else:
+                convs.append({"role": role, "content": str(obj)})
         return convs
 
     def add_user_input(self, question):

api/apps/api_app.py

                                                        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

                     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

     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: