Deterministic Replay

Any shot or campaign can be re-executed against the recorded event stream to reproduce exactly what orchestration saw and decided.

Replay as ground truth

Because the event log is the single source of truth and procedure logic is deterministic, orchestration can re-run any past shot bit-for-bit. Feed the recorded events back into the same procedure version and it reaches the same states and would emit the same commands. This is the core tool for post-shot analysis on the breeder and for validating orchestration changes before they touch either machine.

Requirements for determinism

• All external inputs (sensors, twin predictions, timers, random seeds) are captured as events, never read live during replay.
• Procedure code has no hidden clock or nondeterministic branch; time advances by recorded events.
• Schema versions are pinned, so old events deserialize with the schema that produced them (see schema evolution).

def replay(shot_id, procedure_version):
    events = log.read(correlation_id=shot_id)   # exact recorded stream
    engine = Engine(procedure_version, mode=REPLAY)  # commands are captured, not sent
    for e in events:
        engine.apply(e)
    return engine.emitted_commands, engine.final_state

# assert replayed commands == originally logged commands  (regression guard)

What-if replay

A variant, covered in replay and what-if simulation, swaps in a new procedure or twin version and replays historical inputs to ask: would the change have behaved better on last week's breeder disruption? Emitted commands are captured, never sent, so the machine is untouched.

Auditable causality

Replay is bound to the decision-lineage bus: causation and correlation IDs let an investigator reconstruct the full chain from a raw diagnostic sample through a twin prediction and a copilot proposal to the gated command that moved a burner plug magnet. Determinism turns 'why did it do that' from a guess into a reproducible experiment.

On both machines this discipline is validated today against synthetic and simulated campaigns, long before FOAK first tritium around 2030.