Pakistan, Sept. 10 -- The Houthi barrage on southern Saudi Arabia has emerged as an operational test for the Makkah Joint Defence Agreement barely a month after it was signed. Tuesday's missile and drone attacks hit Aramco facilities and an airbase across four Saudi cities, injured 73 people and pushed a Yemen conflict that Riyadh had spent years trying to contain back across the border. Defence Minister Khawaja Asif has now said that further spillover could bring the Pakistan-Saudi-Turkiye pact into operation.

What that means needs defining before another round of missiles decides it for the three capitals. The agreement signed on August 7 commits its members to regard an armed attack on one as an attack on all. Yet its public text does...