camera: per-platform capture-orientation extension + macOS sensor=0

macOS preview was stretching (aspect wrong) and macOS photo capture
was rotating the landscape sensor 90° because the shared
PhotoOutput / CameraInstance code was setting
`AVCaptureConnection.videoOrientation` from the orientation snapshot
unconditionally. iOS needs that to rotate sample buffers to portrait;
macOS desktop cams are physically landscape and any rotation just
skews the result.

Moved the rotation call behind a per-platform extension on
`AVCaptureConnection`:
  - `ios/Classes/Camera/AVCaptureConnection+iOS.swift` applies the
    snapshot orientation (current behavior).
  - `macos/Classes/Camera/AVCaptureConnection+macOS.swift` is a
    no-op. macOS-flavoured photos / preview frames now flow at
    native landscape orientation.

`CaptureDevice` reports sensorOrientation=0 on macOS (was hardcoded
90 for iOS); on macOS the page's `normalizeCameraCapture` math then
collapses to identity and the saved JPEG stays the landscape the
sensor produced. iOS keeps sensorOrientation=90 (matches
camera_avfoundation's reported value and the existing capture-
transform math).

Photo and video paths now both produce upright content on macOS
(video already worked because VideoRecorder's transform table maps
the always-portraitUp macOS snapshot to `.identity`).

darwin/Camera/CameraInstance.swift

@@ -425,10 +425,9 @@ final class CameraInstance {
             // front camera — raw sensor feed at capture, mirror as a
             // playback decision.
             if let videoConn = videoDataOutput?.connection(with: .video) {
-                if videoConn.isVideoOrientationSupported {
-                    videoConn.videoOrientation = lockedOrientation?.avVideoOrientation
-                        ?? orientation.current.avVideoOrientation
-                }
+                videoConn.applyUxCaptureOrientation(
+                    lockedOrientation ?? orientation.current
+                )
                 if videoConn.isVideoMirroringSupported {
                     videoConn.automaticallyAdjustsVideoMirroring = false
                     videoConn.isVideoMirrored = false
@@ -457,11 +456,8 @@ final class CameraInstance {
     }
 
     private func applyVideoOrientationOnPreview(_ next: DeviceOrientationFlutter) {
-        guard let conn = videoDataOutput?.connection(with: .video),
-              conn.isVideoOrientationSupported else {
-            return
-        }
-        conn.videoOrientation = next.avVideoOrientation
+        videoDataOutput?.connection(with: .video)?
+            .applyUxCaptureOrientation(next)
     }
 
     private func emit(_ extras: [String: Any]) {

darwin/Camera/CaptureDevice.swift

@@ -28,18 +28,22 @@ enum CaptureDevice {
                 DiscoveredCamera(
                     device: device,
                     lens: lensName(for: device.position),
-                    // iOS doesn't expose sensor orientation directly;
-                    // 90° matches what `camera_avfoundation` reports
-                    // and what banlu's `normalizeCameraCapture` math
-                    // assumes for iOS sensors. macOS desktop cameras
-                    // are already landscape — 0 is the right answer
-                    // there but the value is unused on macOS (no
-                    // recording rotation, no preview rotation).
-                    sensorOrientation: 90
+                    sensorOrientation: defaultSensorOrientation
                 )
             }
     }
 
+    /// Hardcoded per platform: 90° on iOS (matches the value
+    /// `camera_avfoundation` reports and that banlu's
+    /// `normalizeCameraCapture` math assumes), 0° on macOS (desktop
+    /// cams are already physically landscape — any non-zero value
+    /// would make `normalizeCameraCapture` rotate the saved JPEG).
+    #if os(iOS)
+    private static let defaultSensorOrientation = 90
+    #else
+    private static let defaultSensorOrientation = 0
+    #endif
+
     /// Per-platform set of device types the discovery session asks
     /// for. iOS only has the built-in cameras; macOS additionally
     /// surfaces externals + Continuity Camera (iPhone-as-webcam).

darwin/Camera/PhotoOutput.swift

@@ -34,9 +34,12 @@ final class PhotoOutput {
             )))
             return
         }
-        if connection.isVideoOrientationSupported {
-            connection.videoOrientation = orientation.avVideoOrientation
-        }
+        // Rotation handled per-platform: iOS applies the snapshot
+        // orientation to the connection (which rotates the captured
+        // JPEG); macOS is a no-op (desktop cams are physically
+        // landscape, any rotation skews the photo). See
+        // `AVCaptureConnection+iOS.swift` / `…+macOS.swift`.
+        connection.applyUxCaptureOrientation(orientation)
         // The recorded photo carries no mirror; mirroring is a
         // preview-only concern.
         if connection.isVideoMirroringSupported {
@@ -57,12 +60,12 @@ final class PhotoOutput {
         }
 
         let delegate = PhotoCaptureDelegate { [weak self] result in
-            // Reset orientation on the photo connection so a future
-            // capture without a snapshot defaults to portrait.
-            if let conn = self?.avOutput.connection(with: .video),
-               conn.isVideoOrientationSupported {
-                conn.videoOrientation = .portrait
-            }
+            // Reset orientation back to portraitUp on the photo
+            // connection so a follow-up shot without an explicit
+            // snapshot defaults cleanly. No-op on macOS (the
+            // extension method is empty there).
+            self?.avOutput.connection(with: .video)?
+                .applyUxCaptureOrientation(.portraitUp)
             self?.inFlight = nil
             DispatchQueue.main.async { completion(result) }
         }

ios/Classes/Camera/AVCaptureConnection+iOS.swift

@@ -0,0 +1,16 @@
+import AVFoundation
+
+/// Per-platform shim for applying capture-time rotation to an
+/// `AVCaptureConnection`. On iOS the connection's `videoOrientation`
+/// genuinely rotates the sample buffers / captured photo; on macOS
+/// it appears to rotate stills but not preview/data-output, AND
+/// desktop cameras are physically landscape so any rotation skews
+/// the result. The macOS counterpart in
+/// `macos/Classes/Camera/AVCaptureConnection+macOS.swift` is a no-op.
+extension AVCaptureConnection {
+    func applyUxCaptureOrientation(_ orientation: DeviceOrientationFlutter) {
+        if isVideoOrientationSupported {
+            videoOrientation = orientation.avVideoOrientation
+        }
+    }
+}

macos/Classes/Camera/AVCaptureConnection+macOS.swift

@@ -0,0 +1,17 @@
+import AVFoundation
+
+/// macOS counterpart of `AVCaptureConnection+iOS.swift`.
+///
+/// macOS desktop cameras are physically fixed landscape — applying any
+/// `AVCaptureVideoOrientation` would skew the captured photo (and on
+/// some macOS versions the preview's data-output buffers) by 90°.
+/// The orientation snapshot from Flutter (always `portraitUp` on
+/// macOS — desktops don't rotate) is therefore ignored at the
+/// connection layer; the recorded video's track transform is still
+/// `.identity` from VideoRecorder's existing mapping, so video stays
+/// landscape too.
+extension AVCaptureConnection {
+    func applyUxCaptureOrientation(_ orientation: DeviceOrientationFlutter) {
+        // Intentionally empty.
+    }
+}