Summer is here, officially. There are signs: There’s the solstice of course, and the L.G.B.T. Pride March. But there are more subtle markers around the city: conviviality on fire escapes; weekends that are thinner with locals and thicker with tourists; and no one wears a thing. This last ritual was challenged on June 23 as writers, agents and editors ambled uptown to celebrate the second anniversary of the literary magazine The Drift, hosted at the David Zwirner gallery on East 69th…