ViewModel.swift

@MainActor final class ViewModel: ObservableObject {
  func prepare() {
    Task {
      do {
        async let wallpaperData = service.fetchImageData(id: "blue_wallpaper")
        async let overlayData = service.fetchImageData(id: "gradient_overlay")
        self.backgroundImage = try await ImageProcessor.merge(background: wallpaperData, overlay: overlayData)
      } catch {
        // TODO: present/handle error
      }
    }
  }
}
struct ImageProcessor {
  static func merge(background: Data, overlay: Data) throws -> UIImage {
    // …
  }
}