Expand description
Transport-free A2UI artifact-schema enumeration.
The embedded control plane had no A2UI surface at all — a client could not ask which artifact schemas the runtime knows how to render.
This matters for a specific, observed reason: an A2UI surface has never appeared in any device certification dump in this suite, because nothing on a mobile build emits an artifact. Being able to LIST the registered schemas separates “the renderer supports nothing” from “nothing produced an artifact this run” — two very different diagnoses that currently look identical.
Read-only by design. Registering a schema mutates how every future artifact renders, so it belongs to composition at build time rather than to an admin call that could change rendering behaviour mid-session.