Not Every Byte Gets a Vote

5 hours ago

Deterministic replay requires recording inputs and running the same ticks to compare results, but not all state should be included in checksums.
Checksums should only cover authoritative gameplay state that can change future outcomes, like player health, projectile position, and RNG state.
Debug data, render interpolation, and certain caches should be excluded from checksums to avoid false replay failures from harmless changes.
The tick system enforces a fixed phase order to provide clear checkpoints for checksums, ensuring replay consistency.
Replay focuses on verifying that seed and inputs lead to the same authoritative state, while snapshots serialize state for save/load, which may include caches.
Derived state, like pathfinding caches, is acceptable but must have explicit contracts, being rebuilt deterministically before use or included in checksums.
Events are outputs that describe committed work and should not affect gameplay; render uses sim facts for presentation without inferring gameplay logic.
A checklist helps categorize new state as authoritative, snapshot, observation, or presentation, narrowing bug searches and improving maintainability.

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