ios-performancelisted

# iOS Performance Optimization Skill ## Core Rules 1. **Use `[weak self]` in escaping closures by default** — use `[unowned self]` only when the closure's lifetime is strictly shorter than the captured object (e.g., parent owns child, child's closure references parent). 2. **Non-escaping closures do NOT need `[weak self]`** — `map`, `filter`, `forEach`, `reduce`, `compactMap`, `sorted(by:)` are non-escaping. The closure executes synchronously and releases captures immediately. 3. **Delegates must be `weak var`** — the delegate protocol must conform to `AnyObject` (or be marked `@objc`). Strong delegates create retain cycles between owner and delegate. 4. **Use `@Observable` over `ObservableObject`** (iOS 17+) — `@Observable` tracks property access per-view, so only views reading a changed property re-evaluate. `ObservableObject` with `@Published` invalidates ALL observing views on ANY published property change. 5. **Break SwiftUI views into small subviews** — each subview localizes its state dependency, so changes only re-evaluate the subview, not the entire parent body. 6. **Use `LazyVStack`/`LazyHStack` inside `ScrollView` for large collections** — `VStack` evaluates ALL children upfront. Use `List` for very large datasets (10,000+) since it reuses cells. 7. **Use `.task` modifier instead of `.onAppear` + `Task {}`** — `.task` automatically cancels when the view disappears. Use `.task(id:)` to restart when a dependency changes. 8. **Profile with Instruments BEFORE optimiz