D016 - Validation separated from effects

Status: decided Date: 2026-08-19

Where it fits, a decision is a pure function and its effect is a thin wrapper that calls it: AddressSpace::validate decides, reserve validates and then acts.

Why: most effects here - mapping memory, entering guest code - are hard to test. A pure decision function makes the rules fully testable without touching the host.

Rejected:

• Decision and effect in one function: the rules are tested only by running the effect.