In ‘Happiest Song Plays Last,’ good intentions come with some off-key notes

When we last checked in on Elliot at the end of “Water by the Spoonful,” the middle work in Quiara Alegría Hudes’ three-play Elliot cycle, he was in Puerto Rico with his cousin Yaz scattering the ashes of his beloved surrogate mother, Ginny, and deciding on his future.

Rather than return to Philadelphia…