# Interview — Fork choice and finality

**Q1. What problem does this mechanism solve?**
What happens when two valid blocks compete at the same height? Model two forks and choose the chain with greater accumulated work; distinguish probabilistic confirmation from deterministic finality.

**Q2. What is the naive failure mode?**
Different peers can temporarily see different chain tips.

**Q3. Is this enough for a secure public blockchain?**
No. This lab isolates one mechanism; production needs cryptographic identities, network rules, adversarial validation, consensus and operational safeguards.

**Q4. What would you test?**
Happy path, malformed input, tampering and disagreement or competing histories where relevant.