What is the musnad in «زَيْدٌ قَائِمٌ», and why?

Conditions of the Predicate: Ellipsis, Reconstruction and Expression

• Zayd, since the initial noun must always be the predicate
• Qāʾim, because it conveys the judgment of standing
• The whole clause, because a predicate must always be a full clause
• Zayd is the predicate and qāʾim its subject because the attribute is treated as prior