OUT IN SAN FRANCISCO’S Tenderloin, addicts fumble into corners in pairs, handing off capsules and vials as corner boys stand watch. Dave Eggers, the 44-year-old hyphenate—novelist-publisher-activist; journalist-entrepreneur; graphic designer–screenwriter-husband-father—is out here too, looking to sign a 20-year lease. In 2002, Eggers, along with the educator Nínive Calegari, founded 826 Valencia, an after-school drop-in tutoring center a mile down the road in the Mission District. It shared the floor with McSweeney’s, the publishing company he’d founded in 1998. There, everyone detached from their keyboards around three...