Artificial intelligence has been a big boon for San Francisco real estate. But not enough of one to make up for the broader struggle across the market. The vacancy rate for San Francisco office space reached a fresh record of 34.5% in the second quarter, according to a report Monday from commercial real estate firm Cushman & Wakefield. That’s up from 33.9% in the first quarter, 28.1% in the same period a year ago and 5% before the pandemic.