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

@@ -13,15 +13,11 @@
 #  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
@@ -260,8 +256,10 @@ class Canvas(ABC):
     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):