The idea is that the sync state corresponding to each client replica is also stored in the server, so the server knows how to respond for interrupted syncs. I.e. the server will only send documents up to the generation corresponding to that sync. See `leap.soledad.server.sync.SyncExchange.find_changes_to_return()`: https://github.com/andrejb/soledad/blob/feature/5517_split-sync-post/server/src/leap/soledad/server/sync.py#L251