How is safety ensured for cross-subnet call execution?

• A. Cross-subnet calls skip validation for speed.
• B. Validation is performed by a centralized authority.
• C. Finalization occurs only on the sender subnet.
• D. Cross-subnet calls are validated by each subnet’s validators and finalized according to that subnet’s rules.

Answer: (D)

Cross-subnet safety comes from validators in each involved subnet checking the message and applying its own finalization rules. When a cross-subnet call happens, validators on the destination subnet (and any relevant intermediaries) validate the call against that subnet’s state and invariants. Only after this validation does the call get finalized according to that subnet’s finalization criteria. This distributed validation ensures no single authority can override subnet rules, and it keeps state consistent across subnets. Skipping validation would undermine safety, and finalizing only on the sender would leave the destination unchecked.