DownloadCancelledException
Thrown when the user cancels a platform-native save dialog (e.g. iOS's FileKit.openFileSaver() document picker) instead of a real transfer/write failure — used by dev.catbit.mosaic.core.data.schemas.event.events.networking.DownloadFileEventSchema's runner to fire onFailure() with no data, matching the convention already used by OpenFilePickerEventRunner for picker cancellation.