TOKYO — Since 2013, Governor Haruhiko Kuroda has been morphing the Bank of Japan into the world’s biggest hedge fund – and, all in all, it’s not going well. On Saturday (April 8), Kuroda will leave BOJ headquarters, handing successor Kazuo Ueda the worst job in international finance. As Ueda gets to work, all eyes are on how he plans to manage the BOJ’s ginormous bet on Japanese government bonds — it owns more than 52% of the market — and stem mounting losses. Yet that may be the easy part. Far more challenging is how BOJ Advisors LLC plots an exit from its massive and market-warping long position in Japanese stocks. That is, even if it can find a way out of this titanically large trade.