N17Q separated historical reconstruction from live execution so a replay could reproduce decisions, tool results, and failures without repeating an external delivery.
#replay
N17Q branched from immutable checkpoints to vary one model, policy, prompt, tool, or failure while preserving the original trace and refusing causal overclaim.
A missing N17Q replay fixture once reached a live read service; the repair removed fallback capability and made incomplete simulated worlds stop visibly.
N17Q made live capture and deterministic replay mutually exclusive runtime modes, so a missing fixture could never fall through to a real tool and repeat an external effect.