Banning WeChat, the world’s most-used messaging app, has the potential to upend the international businesses of companies from Apple Inc. to Walmart Inc. and shut down personal communications between America and China. The White House’s vaguely worded edict left a lot of open questions about how broadly the ban would be applied and the full ramifications for Tencent Holdings Ltd. But it likely gets WeChat bumped off Apple and Google’s app stores in 45 days, which means at least suspending updates for a service vital to everything from engineers talking with iPhone assemblers to Chinese people video-chatting with family back home.