Is the Readonly module forcing the variables into the global space? Surely that would be something terrible.

There is no such thing. main:: could be considered the root namespace, but it's no more or less global than any other namespaces.

Furthermore, Readonly doesn't move or create variables. It simply alters the variable you pass to it to make it readonly. If you pass it a variable in the main:: namespace, it'll affect a variable in the main:: namespace. If you pass it a variable in the Foo::Bar:: namespace, it'll affect a variable in the Foo::Bar:: namespace. It you pass it a lexical variable, it'll affect the lexical variable.