Authors XCUIest UI tests for iOS / iPadOS / tvOS and macOS desktop apps - uses the three-class XCUIApplication / XCUIElement / XCUIElementQuery pattern, sets accessibility identifiers on production code, runs via `xcodebuild test` with destination, parses the `xcresult` bundle. The macOS desktop delta (platform=macOS destination flags, TCC privacy-permission resets, per-device performance baselines) is in references/macos.md. Use when an iOS or macOS app needs UI tests in Apple's first-party framework (no external runtime; native to Xcode).