Workaround to finding a better way to -setUbiquitous…
See -[DocumentsListController(Making) copyDocumentMetadataPlistToICloud:] .
I’m calling this instead of --[DocumentsListController(Making) setUbiquitous:] , but at the same place: after creating, saving and closing a newly created document.

This workaround seems to succeed, and I haven’t encountered any Core Data errors (in just a very few trials).
Still bothersome: as before, if one device creates such a document before the app launches on a peer device, the peer device discovers the document, but can never open it.

NOTE: this version needs cleanup (removal of exploratory methods and other thrashing).