Document orientation policy and emulator-testing pitfalls in CLAUDE.md

Capture two things future sessions need to know up front: (1) the
activity is locked to portrait and the camera image stays in the
device frame on purpose — eight releases of orientation-tracking
attempts (v1.1.6 → v1.1.13) all got reverted, and per-orientation
correctness now lives in the EXIF tag rather than the GL pipeline; (2)
the Pixel 6 emulator's default virtual scene is too symmetric to
verify rotation visually, `emu rotate` decrements rather than
increments, and there is a startup window where camera bitmaps look
black.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -86,6 +86,21 @@ Bitmaps emitted to `StateFlow`s are **never eagerly recycled** immediately after
 - Error/success dismiss indicators use cancellable `Job` tracking to prevent race conditions
 - `writeExifToUri()` returns boolean and logs at ERROR level on failure
 
+### Orientation policy (do not change without asking)
+
+- Activity is `screenOrientation="portrait"` in the manifest. The GL surface and Compose layout therefore never rotate.
+- The camera passthrough uses a fixed 90° texcoord rotation (`texCoordsBack`/`texCoordsFront`). There is no `setTargetRotation`/`setDisplayRotation`/`getTransformMatrix`-based rotation tracking — past attempts (v1.1.6 through v1.1.13) all introduced subtle bugs and were reverted.
+- The camera image lives in the device's portrait frame and visually follows the phone as it tilts. Per-orientation correctness comes from the EXIF orientation tag written at capture (`OrientationDetector.degreesToExifOrientation(rotationToDegrees(deviceRotation), isFrontCamera)`), not from rotating the bitmap.
+- `OrientationEventListener` (`viewModel.currentRotation`) is for EXIF only. It is **not** the same as `Display.rotation`: it fires at the 45° tilt threshold while the activity rotates later, so it must not drive anything that has to stay in sync with the GL surface.
+- `SurfaceTexture.getTransformMatrix()` with a custom `SurfaceProvider` does not change on `Preview.targetRotation` updates; rebinding doesn't reliably help either. Don't go down that road again.
+
+### Local Android testing
+
+- AVD: `tilfluktsrom` (Pixel 6, API 35, Google APIs) at `~/.android/avd/`. Boot with `emulator -avd tilfluktsrom -no-snapshot-save -gpu swiftshader_indirect -no-audio`.
+- `adb -s emulator-5554 emu rotate` cycles `ROTATION_0 → 3 → 2 → 1 → 0` (decrements by 90°), not the other way.
+- The default virtual scene is too rotationally symmetric to verify which way is "up". For orientation testing, pass `-virtualscene-poster wall=/path/to/marker.png` and ensure the scene camera faces the wall, or just don't trust emulator screenshots as proof of correct orientation.
+- Camera bitmaps captured at startup tend to look black for a few seconds while CameraX rebinds. Wait ≥10 s after `am start` before screenshotting.
+
 ## Permissions
 
 | Permission | Purpose | Notes |