RIGHT ABOUT NOW, all over America, a couple hundred thousand runners are beginning to train for fall-marathon season. To them, the most important marathon is the one that’s ahead, whether it’s in Chicago or New York or Philly or Pensacola. But the most meaningful 26.2-miler of the year—perhaps of the century—was run on April 21. On Patriots’ Day in Boston, I rode in the press truck covering the women’s lead pack, tweeting 100-something times about Shalane Flanagan, who graced our front cover in May and led the race from the gun. She ran a three-minute PR (2:22:02) and an American record for the course but finished seventh, after carrying repeat champ Rita Jeptoo and the rest of the lead pack through a torrid first 20 miles. It was a great,…