Event sourcing
Storing what happened rather than what is currently true, so any past state can be reconstructed. Built it for a regulator; keep reaching for it for agents.
Also called event-sourced, append-only log
The system stores an append-only log of events. Current state is a projection you can recompute. Nothing is overwritten, so any moment in the past can be reconstructed exactly.
I led a ground-up rewrite onto this architecture under SEC guidelines. We had to reconstruct the complete state of any agent's account at any point in time from the design itself, not approximately or from backups.
Agent systems keep missing this idea. They usually store memory as current state: a summary, compacted context, or a file that gets rewritten. Each update destroys part of the record that led to it. You cannot properly audit a decision if you cannot replay how the system reached it.
Compliance engineering solved this in the 1990s. The field is currently reinventing it badly.
See also Verification and Comprehension debt.