"Build a great camera experience for iPhone Duo" covers the device open and the device closed, including reconfiguring the session from AVCaptureDeviceDirectionCoordinator's change handler when the forward-facing camera changes. It does not cover the partially open pose, which "Leverage multiple displays and scenes on iPhone Duo" treats as a first-class hinge state with a continuous angle. Consider a camera app that keeps a live preview on screen and adopts AVCaptureDevice.RotationCoordinator — the documented remedy for cases like the square front sensor on iPhone 17, where a hard-coded 90° leaves the preview tilted — applying videoRotationAngleForHorizonLevelPreview to both the preview and the capture connection. In the partially open pose the two halves are at different physical attitudes: one stands up, the other lies flat. Which camera does AVCaptureDeviceDirectionCoordinator report as forward-facing while the hinge status is partially open? Does the hinge angle affect that decision? RotationCoordinator derives its angle from device attitude. With the two halves at different attitudes, which one does videoRotationAngleForHorizonLevelPreview reflect — the half carrying the active camera, the half hosting the preview layer, or a single device-level reference? If an app deliberately keeps the rear camera on the scene while its preview is drawn on the half facing the user, is that a supported configuration, or is the coordinator expected to override that choice? Is any of this modelled in the iPhone Duo simulator, or does the partially open pose require real hardware to test? Question 4 matters for planning: building against a rotation value that only appears on device would be worth knowing about before the hardware ships.