including a comprehensive safety sweep prior to boarding, and the pilots, mechanics and safety leaders deemed the aircraft entirely safe to fly.”
Considering it's about 20 feet in the air, the most likely people to have done it would have been "mechanics" (APU oil top up? Nav/strobe light relamps?). If it was cleaners, they didn't do a very good job
So you get those same (unprofessional) mechanics to safety sweep the aircraft? How is that going to allay the fears of the flight attendants?