EUGENE, Oregon – The moment was both majestic, and at the same time lacking in appropriate majesty. Majestic, because the athlete was Allyson Felix, at 36 years old, the most decorated woman ever in track and field, running the last competitive lap of her life and adding yet another medal to the heaviest collection in the sport’s long history. Lacking in majesty, because the event was the second leg on a mixed 4×400-meter relay on the first night of the 18th Track and Field World Championships, but the first in Felix’s home country, in a city where she could apply to receive mail, because she has raced here so often and so brilliantly. And because the United States won a bronze medal, not gold, a minor quibble in the end.