Error Handling

Solidity provides three mechanisms for error handling: `require()` validates inputs and conditions (refunds remaining gas), `revert()` with custom errors is gas-efficient, and `assert()` checks for invariants that should never be false. Custom errors (introduced in Solidity 0.8.4) save gas: `error InsufficientBalance(uint256 available, uint256 required);`. Use `try/catch` for handling errors from external calls. All state changes are reverted on error.