On November 14, 1943, Bruno Walter, scheduled to guest-conduct the New York Philharmonic, came down with the flu hours before a national radio broadcast. As this Carnegie Hall program indicates, Leonard Bernstein, the orchestra’s brand-new assistant conductor, stepped in. The Times put the story on the front page the next day (calling the 25-year-old a “young aide”), and Bernstein’s career was launched. The Philharmonic will celebrate the 65th anniversary of Bernstein’s debut this Friday.