A line in Sunday’s program notes said it all: “The two men shared an aesthetic soul: both prized suggestion over statement, atmosphere over argument, and the shimmer of a moment over its tidy resolution.” Those words described the uniquely French collaboration between composer Claude Debussy (1862-1918) and Paul Verlaine (1844-1896), anticipating what turned out to be an exquisite performance of their 1887 “Ariettes oubliées” or “Forgotten Little Songs.” “Songs of Longing and Lush Summer” was...