Amazing! Curious about whether you faced an issue with latency? What if two people are concurrently editing the same item on the whiteboard with high latency?
What do you mean by "the same item" ? You cannot really "edit" things other people drew. You can delete something as someone else is drawing it. Then it doesn't really matter if the other person continues drawing, the item will eventually be deleted.
If you start drawing with the pencil and your line is erased before you finish, a new line looks to be started, with different properties (black and a certain thickness).