Nobody else seems to care but I think nostr finally needs a Hash Chain event kind or tag that is enforced server-side:

- To add a new event to the chain, you MUST reference a previous event. If the referenced event does not exist, you get an error.
- Only one event can reference another event. If an event has already been referenced before, you get an error.

IMO (almost) solves the biggest issue with nostr which is the fact that you never know if the data you have is complete and it allows atomic updates of data. Suggestions for improvements of this idea welcome.