Keys absent from settingsRegistry resolve through the user-scope path and return an empty effective_value, which Apple clients interpreted as false — flipping these default-ON toggles off on first sync. Register both device-scoped keys with default "true" so defaults resolve correctly and device overrides round-trip. seek_cache_enabled had been syncing unregistered since it shipped; dolby_vision_enabled is new (Apple client Dolby Vision toggle, silo-apple e9bd775). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>