Runtime introspection key, independent of the fluent method name.
const labels = defineExtension({
string: {
label: defineMetadataMethod('label').argument<string>(),
internal: defineMetadataMethod('visibility').value('internal')
}
});
const s = withExtensions(labels).string().label('Title').optional();
type Label = InferExtensionMetadata<typeof s>['label']; // 'Title'
Define an immutable metadata-only method for use inside
defineExtension().Unlike ordinary extension methods, its stored value is also available through
InferExtensionMetadata<S>. Repeated writes replace the value for that key. The method does not validate input or change the schema's inferred value type. Methods are installed only on factories returned bywithExtensions().