space.ziran.checkpoint

An atile-style published snapshot of a document, written by any member into their own repo (rkey = the doc's rkey; putRecord replaces the author's previous checkpoint). Carries the tile manifest with every resource's src replaced by an atproto blob ref, so an invitee can instantiate the document without replaying history, then apply ops past the frontier. Checkpoints are rare: go-live, a size threshold, or an explicit publish.