Standing beside the keeper’s cottage on the tip of Gurnet Point, with Plymouth Harbor spread out below and Provincetown visible across the bay, Dolly Snow Bicknell began her tour not with a history lesson, but with a poem. Written by Edgar Guest, The Lightkeeper Wonders imagines a lighthouse keeper confronting automation after decades of tending a light by hand. Near the end, the keeper asks: “And I wonder now — will the grass stay green,Will th…