In public, President Vladimir V. Putin of Russia says his country’s growing friendship with China is unshakable — a strategic military and economic collaboration that has entered a golden era. But in the corridors of Lubyanka, the headquarters of Russia’s domestic security agency, known as the F.S.B., a secretive intelligence unit refers to the Chinese as “the enemy.” The threats are laid out in an eight-page internal F.S.B. planning document, obtained by The New York Times, that sets priorities for fending off Chinese espionage. The document is undated, raising the possibility that it is a draft, though it appears from...