You're right that if you tried to do something like this using record/replay, you would pay an enormous cost. Antithesis does not use record/replay, but rather a deterministic hypervisor (https://antithesis.com/blog/deterministic_hypervisor/). So all we have to remember is the set of inputs/changes to entropy that got us somewhere, not the result of every system operation.
The classic time space tradeoff question:
If I run Antithesis for X time, say 4 hours, do you take periodic snapshot / deltas of state so that I don't have to re-run the capture for O(4 hours) again, from scratch just to go back 5 seconds?
