How long can Japan’s central bank defy global market forces?

There’s a Chinese proverb that holds it is better to plan one’s means of retreat than 36 different ways to win the battle.

It’s an axiom that has cropped up on Tokyo trading floors this autumn, after Japan lavished a record $62bn to fight the yen’s collapse below a three-decade low, in as many as four separate interventions since September.

It’s only one front in its war against global market forces. By the end of June, after months…