adds
private fun adds(access: Int, desc: String?, notAdded: Set<String>, vararg annotations: List<AnnotationNode>?): Boolean
Whether a mixin's own member is an ADDITION the target then carries under this name.
Public only: everything below it is renamed when @Unique and out of a snippet's reach either way. desc is a method descriptor, or null for a field — a trailing CallbackInfo is a handler by construction, and that is the backstop for one whose annotation did not survive its own build (Quark ships such a method; it lands renamed like every other handler).
Third-party annotations are NOT disqualifying and must not be — @Nullable and a mod's own markers sit on merged members freely. Only what Mixin itself reads decides how a member merges.