Japan is spending five weeks mining the seafloor. It is a technological milestone — and a stress test for how nations balance geopolitics, clean energy demand, and environmental risk. The year 2010 was a reckoning for Japan’s economic security. On September 7, the Chinese fishing trawler Minjinyu 5179 refused an order by Japan’s coast guard to leave disputed waters near the Senkaku Islands, which are known in China as Diaoyu. The vessel then rammed two patrol boats, escalating a decades-long territorial feud. apan responded by arresting the captain, Zhan Qixiong,…