The narrow `<AppKit/NSView.h>` header only forward-declares NSWindow,
so `view.window.backingScaleFactor` fails to compile on macOS with:
error: property 'backingScaleFactor' cannot be found in forward
class object 'NSWindow'
Use the AppKit umbrella header so NSWindow's interface (including
backingScaleFactor) is in scope. Same idiomatic include any non-trivial
Cocoa code reaches for; we're already linking -framework Cocoa so
there's no compile-time cost beyond a slightly heavier translation
unit (the .mm is ~30 lines anyway).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Dion Moult
6b72a60d8c