What is a valid syntactic account of “Zayd qāma”?

Fronting the Subject: Restriction, Reinforcement and the al-Jurjani–al-Sakkaki Debate

• Zayd is mubtadaʾ and the verbal clause is its predicate
• Zayd is the direct object of qāma
• Zayd is a preposition and qāma its object
• Qāma is necessarily an accusative modifier of Zayd