Seems like backgroundassets-debug is not working.
I use backgroundassets-debug -s --app-update --app-bundle-id *** --device-id yyy to test a new BackgroundDownloadHandler. But the console.app tells us that the extension is kill by SpringBoard.
Sandbox: hook..execve() killing com.abc.mtt.badownloadextension[pid=1169, uid=501]: outside of container && not a driver && !i_can_has_debugger
error.log