diff --git a/backend/open_webui/models/chats.py b/backend/open_webui/models/chats.py
index 957492d817..571a3d8378 100644
--- a/backend/open_webui/models/chats.py
+++ b/backend/open_webui/models/chats.py
@@ -569,7 +569,18 @@ class ChatTable:
                 **message,
             }
         else:
-            history['messages'][message_id] = message
+            now = int(time.time())
+            # This upsert is also used for partial streaming/final updates.
+            # If a concurrent whole-chat write dropped the assistant placeholder,
+            # never persist the partial payload as a malformed history node.
+            history['messages'][message_id] = {
+                'id': message_id,
+                'parentId': message.get('parentId'),
+                'childrenIds': message.get('childrenIds', []),
+                'role': message.get('role', 'assistant'),
+                'timestamp': message.get('timestamp', now),
+                **message,
+            }
 
         history['currentId'] = message_id
 
diff --git a/backend/open_webui/utils/middleware.py b/backend/open_webui/utils/middleware.py
index 56226fc226..617f6983ec 100644
--- a/backend/open_webui/utils/middleware.py
+++ b/backend/open_webui/utils/middleware.py
@@ -3582,6 +3582,17 @@ async def streaming_chat_response_handler(response, ctx):
         task_id = str(uuid4())  # Create a unique task ID.
         model_id = form_data.get('model', '')
 
+        def build_assistant_message_update(**fields):
+            return {
+                'id': metadata.get('message_id'),
+                'parentId': metadata.get('user_message_id'),
+                'childrenIds': [],
+                'role': 'assistant',
+                'model': model_id,
+                'timestamp': int(time.time()),
+                **fields,
+            }
+
         # Handle as a background task
         async def response_handler(response, events):
             def tag_output_handler(content_type, tags, output):
@@ -5057,24 +5068,24 @@ async def streaming_chat_response_handler(response, ctx):
                         await Chats.upsert_message_to_chat_by_id_and_message_id(
                             metadata['chat_id'],
                             metadata['message_id'],
-                            {
-                                'done': True,
-                                'content': serialize_output(output),
-                                'output': output,
+                            build_assistant_message_update(
+                                done=True,
+                                content=serialize_output(output),
+                                output=output,
                                 **({'usage': usage} if usage else {}),
-                            },
+                            ),
                         )
                     elif usage:
                         await Chats.upsert_message_to_chat_by_id_and_message_id(
                             metadata['chat_id'],
                             metadata['message_id'],
-                            {'done': True, 'usage': usage},
+                            build_assistant_message_update(done=True, usage=usage),
                         )
                     else:
                         await Chats.upsert_message_to_chat_by_id_and_message_id(
                             metadata['chat_id'],
                             metadata['message_id'],
-                            {'done': True},
+                            build_assistant_message_update(done=True),
                         )
 
                 # Send a webhook notification if the user is not active
@@ -5127,17 +5138,17 @@ async def streaming_chat_response_handler(response, ctx):
                             await Chats.upsert_message_to_chat_by_id_and_message_id(
                                 metadata['chat_id'],
                                 metadata['message_id'],
-                                {
-                                    'done': True,
-                                    'content': serialize_output(output),
-                                    'output': output,
-                                },
+                                build_assistant_message_update(
+                                    done=True,
+                                    content=serialize_output(output),
+                                    output=output,
+                                ),
                             )
                         else:
                             await Chats.upsert_message_to_chat_by_id_and_message_id(
                                 metadata['chat_id'],
                                 metadata['message_id'],
-                                {'done': True},
+                                build_assistant_message_update(done=True),
                             )
 
                 try: