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Take a non-trivial React app with a measurable render-performance problem and fix it with evidence: profile with the React DevTools Profiler to find the real cause, fix it structurally (move state down, pass children, split components) before reaching for memo, and justify any memoization with before/after measurements. Cover key behavior with React Testing Library tests that query by role/text and survive refactors.
A real bottleneck found by profiling and fixed; before/after evidence; structural fixes preferred over blanket memo.
Re-render causes correctly diagnosed; render-vs-commit understood; state placed at the right level.
RTL tests query by role/text and assert visible behavior; they survive an internal refactor.
Memoization is targeted and justified, not applied everywhere speculatively.
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# Performance-tuned, tested React app (profiled, not guessed) ## Goal Take a non-trivial React app with a measurable render-performance problem and fix it with evidence: profile with the React DevTools Profiler to find the real cause, fix it structurally (move state down, pass children, split components) before reaching for memo, and justify any memoization with before/after measurements. Cover key behavior with React Testing Library tests that query by role/text and survive refactors. ## Acceptance criteria - [ ] Measured optimization: A real bottleneck found by profiling and fixed; before/after evidence; structural fixes preferred over blanket memo. - [ ] Render understanding: Re-render causes correctly diagnosed; render-vs-commit understood; state placed at the right level. - [ ] Behavior tests: RTL tests query by role/text and assert visible behavior; they survive an internal refactor. - [ ] No premature memo: Memoization is targeted and justified, not applied everywhere speculatively. ## Verification - [ ] Document installation and run commands. - [ ] Record automated checks and their exact commands. - [ ] Add representative output, screenshots, or a short demo where useful. - [ ] Confirm failure paths and known constraints. ## Decision log ### Decision title - Context: - Choice: - Alternatives considered: - Tradeoffs: ## Evidence - Link each rubric criterion to the file, test, or artifact that demonstrates it. ## Known limitations - List what is intentionally out of scope and what should be improved next.