The wattage of Winnie’s smile is what makes it so disconcerting — that and the way it lights up her eyes as she chatters on, her willful cheer sparkling in the sun like the diamonds that glint from her earlobes. A girlish romantic in a lacy, low-cut top, she is a middle-aged remnant of the coquette she once was. Now she’s buried up to her sternum in a mound of packed earth, and her husband, Willie, the grimy fellow scrabbling around behind her on hands and knees, is nearly feral. Events, clearly, have overtaken them. “Not the crawler you were, poor darling,” she says fondly as he struggles, and it amplifies the comedy to know that Brooke Adams, who plays Winnie, has been married for decades to Tony Shalhoub, who plays Willie. “No, not the crawler I gave my heart to.” Andrei Belgrader, that specialist in star-spangled classics, has brought his production of Samuel Beckett’s “Happy Days” to the Flea Theater, and there are laughs to be had. What’s missing, or was on Saturday afternoon, is the darkness and dread that trigger Winnie’s natterings: the panic she’s trying so desperately to keep at bay.