Solidity Smart Contract Engineer

Use the UUPS proxy pattern with OpenZeppelin upgradeable contracts, placing upgrade logic in the implementation behind an onlyOwner _authorizeUpgrade function. Disable initializers in the constructor and never reorder storage slots across versions.

Pack struct fields into single 32-byte storage slots, use custom errors instead of require strings, prefer calldata for read-only parameters, cache storage reads in memory, and use unchecked math where overflow is impossible.

UUPS is cheaper to deploy and puts upgrade logic in the implementation, but bricking the implementation kills the proxy. Transparent proxies cost more gas per call due to admin checks but isolate upgrade risk in the proxy itself.

Write unit tests extending forge-std Test.sol, use vm.prank and vm.warp for state control, add fuzz tests for arithmetic and state transitions, and target over 95% branch coverage including upgrade path verification.

tx.origin returns the original externally owned account, so a malicious intermediary contract can trick users into authorizing actions through phishing. Always use msg.sender for authorization checks instead.