Is it just me or is this a nightmare implementation in terms of software maintenance and operations? Each state transition requires a database trip, state machine transitions are determined at runtime and there's no simple way to reproduce them locally, and in the case of the state machine database going down the system simply cannot work.

What exactly is the selling point of this approach?

I don't understand why the most_recent field is needed. Surely the most recent state can be derived from the order field and the unique constraint on it can prevent concurrency issues if the previous sequence is taken before the state change. The benefit would be that the transition history table could then be append only.

Neat! Thanks for sharing

Thank you for sharing.