Solidity interview: 20 questions

Storage, calls, and the things that actually break

1. What is a storage collision in an upgradeable proxy?
2. When does delegatecall write to the caller?
3. How do you pull-pay versus push-pay, and why does it matter?
4. What does unchecked forfeit?
5. Reentrancy: guards vs CEI vs read-only reentrancy.
6. tx.origin versus msg.sender.
7. Oracle manipulation in a two-block window.
8. What is a dusty leftover approval?
9. How do you fuzz a rounding error in a vault?
10. When is send / transfer the wrong tool?
11. Upgrade delays as a feature.
12. Signature replay across chains.
13. Storage packing and griefing.
14. What does a good invariant test look like?
15. How do you reason about MEV on a liquidation?
16. Permit vs approve/permit2.
17. Default visibility mistakes.
18. What belongs in a constructor versus an initializer?
19. How do you write a finding that a protocol engineer will fix?
20. What will you refuse to ship?

Bring a repo, not a list of courses.