Save Element creates new elements (create-on-404); Upload World renamed
with real error surfacing; Rename World pushes; Download World returns
(prefixed-key clean) with self-healing Map/Pin/Marker templates; upload
parser ships links as _id/_ids UUIDs; per-world key resolution ends the
wrong-world write class; scoped keys primary in all copy.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>