> I assume java gets around this by bundling libraries into the deployed .jar file. That this is better than a lock file, but doesn't make sense for scripting languages that don't have a build stage. (You won't have trouble convincing me that every language should have a proper build stage, but you might have trouble convincing the millions of lines of code already written in languages that don't.)

You are wrong; Maven just picks one of lib-x:0.1.4 or lib-x:0.1.5 depending on the ordering of the dependency tree.