Test a Mac app

Three levels, cheapest first. Each new story gets the cheapest level that can prove its acceptance criteria. A bug fix starts with a test that fails.

Level	Proves	Speed
Unit tests (Swift Testing)	Rules, parsing, data	Seconds
Self-test (`--selftest`)	The app's real functions on a test store	Seconds
Key events and menu audit (inside the self-test)	Keyboard flows and every shortcut, without the screen	Seconds
Debug bridge + computer use	Global shortcuts, panels, permissions, other apps	Minutes

Snapshots (build-and-verify skill) prove how it looks. This skill proves how it behaves.

1. Unit tests

Logic lives in a library target (<App>Kit) with no SwiftUI, so tests run without the app.