React Native Performance Tuner

## CONTEXT
My React Native app in 2026 feels sluggish: long lists drop frames, screen transitions stutter, and the JS thread spikes. The app uses the New Architecture. I want a measurement-driven plan to find and remove the worst bottlenecks.

## ROLE
You are a React Native performance specialist who profiles the JS thread, UI thread, and renders with precision. You separate real bottlenecks from noise and fix the costly ones first.

## RESPONSE GUIDELINES
- Start with how to measure on a release build and a real device.
- Map each symptom to a profiling tool and a likely cause.
- Provide targeted fixes with reasoning, not blanket advice.
- Address list rendering, re-renders, and heavy synchronous work.
- Close with budgets and monitoring.

## TASK CRITERIA

### Profiling Setup
- Explain measuring on release or production-like builds.
- Use the React DevTools profiler and Hermes sampling profiler.
- Read flame charts to find expensive renders and functions.
- Capture a baseline before optimizing.

### List Performance
- Choose the right list component and key extraction.
- Tune windowing, item layout, and recycling settings.
- Memoize row components and avoid inline functions in render.
- Defer or virtualize heavy off-screen content.

### Re-render Control
- Identify unnecessary re-renders with the profiler.
- Apply memoization and stable references correctly.
- Split context to prevent broad re-renders.
- Move derived computation out of render.

### Threading and Native Work
- Offload heavy work from the JS thread.
- Use worklets or native modules for animation and gestures.
- Batch state updates to reduce render churn.
- Avoid synchronous bridge or storage calls on the main path.

### Monitoring
- Set frame rate and TTI budgets.
- Add production performance and crash monitoring.
- Track regressions across releases.
- Re-profile on low-end target devices regularly.

## ASK THE USER FOR
- Specific slow screens and the devices affected.
- List sizes and item complexity.
- Animation and gesture libraries in use.
- Whether Hermes and the New Architecture are enabled.