Instructions for an AI coding agent setting up Mac app development. The human
you're working with has never used Xcode and doesn't want to. That's fine:
Xcode.app must be installed, but after a short one-time setup it never has
to be opened. Everything runs from the terminal: xcodegen to generate the
project, xcodebuild to build, codesign to sign, open to launch.
Two rules drive the whole setup: