Which properly distinguishes walāyah from prophetic ʿiṣmah?

Karāmāt al-Awliyāʾ: Extraordinary Gifts and Their Evidence

• Infallibility is not required of a walī; obedience and piety matter
• Every walī is incapable of error
• ʿIṣmah and piety are interchangeable technical terms
• A walī is exempt from religious obligations