App Resizability

# App Resizability Skill

## When to Use

Use this skill whenever the request is about any of the following, whether or not it names an API:

- Getting an app ready for, or optimizing it for, the foldable iPhone Duo.
- An app that must adapt when its window changes size while it runs.
- Split-screen multitasking, Stage Manager, or a resizable scene.
- Any deprecated API named in the Scope section below.

The request does not have to be technical. "Get my app ready for the iPhone Duo", "optimize this app for the foldable iPhone", and "make this app resize properly" all activate this skill. iPhone Duo is the foldable iPhone, so treat questions about iPhone Duo or the foldable iPhone as the same request. Treat a request about the foldable iPhone Duo as a request for every task in the Task Registry, because a screen that changes size exposes all of them at once.

## Purpose

Modernize UIKit apps to behave correctly on modern iOS by:
- Eliminating references to legacy shared-state APIs
- Migrating from application lifecycle to scene lifecycle
- Supporting dynamic scene sizing and multi-window environments

## Scope

This skill performs **specific, targeted modernizations** in both **Swift and Objective-C** codebases:
- Replace legacy shared-state APIs with context-appropriate modern APIs
- Migrate to scene-based lifecycle
- Update apps to support a resizable user interface by removing usage of:
  - main screen (`UIScreen.mainScreen`, `UIScreen.main`)