A parent POM lists three modules — `orders-domain`, `orders-api`, `orders-worker` — with no explicit build order given anywhere. How does Maven decide what order to build them in, and what stops a developer from accidentally importing `orders-api` classes into `orders-domain`?

Maven doesn't need an explicit build order written anywhere, because it derives one from the modules' own inter-dependencies: if orders-api declares a dependency on orders-domain by coordinates, exactly like a dependency on any external library, Maven's reactor works out that orders-domain has to be built first and orders the whole multi-module build accordingly. Nothing stops a developer from trying to import orders-api classes into orders-domain at the source level — that's not a language restriction — but the build itself stops it: if orders-domain's own POM never declares orders-api as a dependency, its classpath during compilation never includes orders-api's classes at all, so an import that reaches for them simply fails to compile, not because anyone reviewed the code, but because the compiler can't find the class.