Determinism is a service contract.

A service contract is a description of what a system will do, and what it will not do, and the conditions under which either statement holds. Determinism is one such condition. Either the system is deterministic under stated inputs, or it is not. There is no middle position.

Probabilistic systems can be made to behave deterministically. The cost is paid in expressivity, in latency, or in apparatus.¹ A studio that wishes to sign a service contract pays the cost. A studio that does not sign service contracts is selling something else.

The trace is the proof. A deterministic system is a system whose trace, replayed against the same inputs, produces the same outputs. The trace format is therefore the system’s first artefact. A trace format is a worldview.

A regulated counterparty does not accept variance as an excuse. The counterparty accepts the variance the contract describes, and refuses the rest. The contract is the boundary.

The position is unfashionable. The position is correct.