Sign in with Bluesky — each stroke you paint becomes a public record on your own PDS (collection com.minomobi.mmopaint.stroke). We ask for the narrowest scope Bluesky's OAuth server accepts today: repo:com.minomobi.mmopaint.stroke — permission limited to this one record type, nothing else on your account. Cryptographically signed by your repo; readable by anyone on the network.
Every stroke records prev_hash → this_hash. Replay all strokes to reconstruct the canvas and verify the chain.