You absolutely get type safety across module boundaries with C in that if provider and user both compile against the same interface, this will be typesafe.

You could even have this type safety on the linker level as far as C is concerned. You just need an object file format that exports C types for symbols. This is not done on any of the (few) systems I know, and probably for practical reasons.

Some other languages give you this link time safety, but I assume at the cost of less interoperable object files.