Update: last_activity updates for all message interactions

- Updates last_activity for both user and assistant messages
- Updates for pipeline executions
- Does NOT update when viewing sessions or history
- Shows true last interaction time (any message activity)

api_routes_v2.py

@@ -596,7 +596,7 @@ def _add_and_mirror_message(chat_id: str, role: str, content: str, file_metadata
     """
     V3 RULE: Append message to S3 conversation.
     MongoDB metadata updated via _save_conversation_to_s3.
-    Only updates last_activity for user messages.
+    Updates last_activity for all messages (user and assistant interactions).
     """
     # 1. Load existing
     current_messages = _load_conversation_from_s3(chat_id)
@@ -620,8 +620,8 @@ def _add_and_mirror_message(chat_id: str, role: str, content: str, file_metadata
     
     current_messages.append(new_msg)
     
-    # 3. Save to S3 - only update last_activity for user messages
-    _save_conversation_to_s3(chat_id, current_messages, update_activity=(role == "user"))
+    # 3. Save to S3 - update last_activity for all message interactions
+    _save_conversation_to_s3(chat_id, current_messages, update_activity=True)
     
     # 4. Auto-generate chat name after first user message
     if role == "user":