Andrew Bailey has two roles with the Red Sox. That’s one too many. As of yesterday, he returned to being the closer — for the fourth time. The moment also marked the return of the most mysterious man on the Red Sox roster. That’s no reflection on Bailey’s personality, which is as sunny, cooperative, good-humored and helpful as anyone in that clubby clubhouse. The mystery with Bailey is that nobody has any idea how long he can stay healthy. It’s a mystery that feels like it should have been solved long ago, but it’s still lingering. And as long as that cloud of uncertainty hovers over Bailey, he is going to have a hard time convincing any of us his return to action means the back end of the Red Sox bullpen is settled. When healthy, Bailey is capable of being as good as nearly any other closer in baseball. He had save totals of 26, 25 and 24 with the A’s from 2009 to 2011. His two-season stint with the Red Sox, however, has been little else besides fits and starts that have been mostly maddening and partly alluring. Witness his excellent April this season. With Joel Hanrahan on board as the closer, Bailey converted his first four hold chances in a row. When Hanrahan was hurt, Bailey stepped in as closer and recorded five saves in a row. His April results are nearly peerless: 1.46 ERA, 0.811 WHIP, .140 batting average against, 20 strikeouts and just four walks. He was going so well that when Hanrahan returned and was ineffective, manager John Farrell handed the job back to Bailey in Toronto at the beginning of the month.