editing a text stack that flows outside of the web content area makes an unusably wide edit popup

there are no maximum bounds on the text editing pane. this is only really a problem when the text stack has a bug that leads it to be much bigger than its parent and flow outside of the content area.

but it should be easy to add a max size check to the editing pane. this makes a buggy stack impact the user less -- so even thought its "coding to the bug" it still seems like the right thing to do.