Which is correct about the initial wāw in “wa-inna ʿalaykum la-ḥāfiẓīn”?

Supplementary Practice 29 — Comparative Rhetoric of Sūrat al-Infiṭār and Sūrat al-Inshiqāq

• Some grammatical analyses take it as circumstantial
• It is necessarily an oath particle
• It is universally deemed meaningless
• It can only coordinate nouns