Kenneth Lonergan makes films about the things that don’t go away. In 2000’s You Can Count On Me, the sudden orphaning of young siblings helps fashion an unsolvable divide between the two in adult life, while in Margaret, which lingered undistributed for years while director and studio fought over the final cut, witnessing a fatal accident sends Anna Paquin’s carefree teenage life spiralling in new, frustrating directions. His third feature as writer-director, Manchester by the Sea, part of Amazon Studios’ effort to chase indie respectability, is Lonergan’s most refined work yet, a restrained but movingly complex portrait of tragedy’s never-ending…