Unimplemented
Marks an OnDeviceLlm that compiles and satisfies the seam but has no real implementation behind it yet — it reports unavailable unconditionally rather than attempting partial/incorrect work. Distinct from UnavailableOnDeviceLlm (a deliberate, permanent "no model on this platform/target" answer): a class carrying this annotation WOULD work once reason (its missing native bridge) is built — see the annotated class's own upgrade-path doc comment.