زَيْدٌ — وَاللَّهُ يَحْفَظُهُ — صَادِقٌ.
Zayd—may God preserve him—is truthful.
The intervening prayer is a parenthetical clause (iʿtirāḍ). Removing it leaves the core predication 'Zayd is truthful' intact. The prayer is neither an obligatory syntactic complement nor a description of the truth claim; it conveys an appropriate additional sentiment.
Do not classify the clause merely by spotting wāw within it. Its position and relative independence from the interrupted grammatical structure establish the parenthetical function.