Frontend: When to Memoize (useMemo / useCallback / React.memo)

> This problem is paper-only - see explanation for the canonical React reasoning. Premature memoization is one of the most common mistakes in React code reviews. The auto-grader validates the decision rules. Given a function call shaped `{ computeCostMs, callsPerRender, isReferentialDep, sourceRowsLargerThan10k }`, return one of: - `"useMemo"` if the value should be memoized (significant compute OR a referential dep, OR working over a large input). - `"useCallback"` if it's a function passed as a prop AND the recipient is React.memo-wrapped (model: `isReferentialDep === true`). - `"none"` otherwise. **Decision tree implemented by the grader:** 1. computeCostMs > 5 → `"useMemo"`. 2. sourceRowsLargerThan10k → `"useMemo"`. 3. isReferentialDep → `"useCallback"`. 4. Otherwise → `"none"`. (If both #1 and #3 hold, useMemo wins - the value itself needs caching.) **For the auto-grader:** implement `memoizationAdvice(input)`.