Why does “jāʾa raʾīsu al-farīqi yafḥaṣu al-akhshāb” appropriately omit circumstantial wāw?

Supplementary Practice 12: Rhetorical Evidence, Competing Analyses and Reasoned Revision

• Wāw is forbidden in every circumstantial sentence
• Yafḥaṣu is a passive past verb
• The clause lacks a referent for the circumstance
• Yafḥaṣu is an affirmative imperfect circumstantial verb with an implicit referential subject