Constrain path dragging

No, there isn't anything liek that. AE's snapping tools are firmly stuck in the 1990s and haven't learned a single trick from other programs. Typically you would use scripts to manipulate masks, paths and their vertices in a controlled manner if you don't want to pull out a ton of guides or create expressions that do the magic. Check AEScripts.com and I'm sure you'll find something that can help you.

Mylenium