The room of a template edited together knows which saved version it holds.
collaboration.version, such as the storage's ETag) and report each save
(collaboration.saved(version)); collaboration.room_version() returns the version the room
holds, to send as If-Match when saving. Without a version from the host nothing changes.ElementSync.seed() writes the window's version to the room's meta map as
version; record_version() writes a saved one. saved() calls it in every window editing
together that may edit, not only the writer: the writer can change while a save is in flight. The
merge on a refused save (412) follows in its own release.