Honor @field(name:) in @error type extra-field accessor matching against handler source class

FieldBuilder.checkErrorTypeSourceAccessors (FieldBuilder.java:2281-2316) verifies that each @error object type’s extra fields (everything except path / message) can be populated from the handler’s source class (the exception class for a GENERIC handler, the DataAccessException-shaped source for a DATABASE handler, etc.). For each (sdlField, sourceClass) pair it calls ClassAccessorResolver.resolve(sourceClass, sdlField.getName(), expectedReturn, …) with the raw SDL name as the accessor base. When the exception’s accessor diverges from the SDL field name ; e.g. an exception exposing getErrorCode() mapped to an SDL field named code, or a Norwegian-named accessor under an English SDL ; the resolver returns Rejected and the type fails classification with no author escape hatch. @field(name:) on the SDL extra field is the natural override: this is structurally the R191 case (free-form Java class as the logical "parent", SDL field bound by accessor name, divergent names need a directive remap). The fix is to read DIR_FIELD on each extra sdlField at :2298-2305 and pass the directive value (when present) as the second arg to ClassAccessorResolver.resolve instead of sdlField.getName(). The directive’s docstring already covers this site under the "underlying-binding target" reading; the docstring update tracked separately should mention @error extra fields as one of the free-form-Java-class accessor-axis examples. No emitter change needed ; ClassAccessorResolver.Resolved.methodName() is the actual reflected method name, so the runtime invocation path is unaffected.