Hezbollah’s flexible chain of command, together with its extensive tunnel network and a vast arsenal of missiles and weapons it has bolstered over the past year, is helping it weather unprecedented Israeli strikes, three sources familiar with the Lebanese militant group’s operations said.Israel’s assault on Hezbollah over the past week, including the targeting of senior commanders and the detonation of booby-trapped pagers and walkie-talkies, has left the powerful Lebanese Shiite militant group and political party reeling.