Write in a local draft, then sign in and snapshot durable revisions straight into your own PDS. There is no live relay or shared server state, so the short link identifies a draft on this device rather than pretending that a browser-only app can coordinate simultaneous writers.
The easy version is local-first: your browser owns the draft, and atproto gives you a durable, portable revision in your repo. That means eventual sharing instead of live multi-writer merging, but it also means there is no product server to keep running or trust.