effectiveDirective
fun effectiveDirective(sourceField: FieldInfo, targetField: FieldInfo, isReverse: Boolean): ConverterDirective?
The directive governing one (source, target) field pairing — owner-anchored: the class that declares the mapping is asked first. That is the source in the forward (@MapTo) direction and the TARGET in the reverse (@MapFrom) direction, whose source is typically a foreign class the user cannot annotate (issue #82). In the reverse direction the source field stays a fallback, so directives placed there keep working. A directive is taken whole (use + onFail together), never merged across the two sides.