In the weeks before a summit that may redefine decades of American commitment to Taiwan, the commanders who would manage any Pacific conflict sat down quietly in Canada to speak plainly with one another. Admiral Paparo and General Yang Zhibin — the men whose forces face each other across the Taiwan Strait — met not to resolve the great tensions between their nations, but to ensure that those tensions do not ignite through misunderstanding. It is an old and necessary ritual: soldiers building the lines of communication that diplomats may soon strain or sever.