During his frequent visits last year as an invited guest at Fenway Park’s season-long centennial bash, Pedro Martinez always made sure to chat with his old friend, Red Sox general manager Ben Cherington. Each time, he found Cherington increasingly dispirited. “I was like, ‘Ben, don’t worry,’ ” Martinez said. “It was a tough season, and he was really stressed out. I just said, ‘Hey, my friend, take it easy. It’s one bad year. We’ve all had a bad year.’ ” If you found it unpleasant to watch the 2012 Red Sox, you should’ve seen the view from Cherington’s chair. The 38-year-old New Hampshire native had worked his way up from an area scout to the general manager’s office, but after 13 years in the organization, his first season in charge of baseball operations turned into a 93-loss nightmare. Cherington wasn’t immune to criticism, but he often seemed like a bystander while manager Bobby Valentine self-immolated and an underachieving, injury-filled roster weighted down for most of the season by bloated long-term contracts caused the Red Sox’ runaway train to crash and burn. That won’t be the case this year. Valentine is gone after only one season, replaced by John Farrell, the manager Cherington wanted all along. And after pulling off last August’s payroll-purging mega-trade with the Los Angeles Dodgers, Cherington overhauled the roster this winter, signing seven free agents and trading for closer Joel Hanrahan. The Sox addressed short-term needs at first base, in the outfield and in the starting rotation and added depth at catcher, shortstop and in the bullpen, all while retaining their greatest assets in a replenished farm system.