Resolves one entry of a registration option that accepts either an instance or a RegistryFactory.

A non-function entry is returned unchanged — the instance arm is byte-identical to the pre-factory behaviour. A function entry is called once with services, and its return value is the result. A throw from the factory is wrapped in an Error whose message names label and whose cause is the original, so a factory that resolves a capability the application forgot to register fails start() naming the option and the entry rather than escaping with a bare registry message.

The discrimination is typeof entry === 'function': no instance of any registration contract is callable, and a class — the one shape that is a function and not a factory — is not assignable to RegistryFactory<T>, so passing one is a compile error rather than a runtime TypeError.