The short version: is it possible to delete helper tools which were set up by the app (SMJobBless() etc.) when the app is deleted? If so, how?
The long version:
The Mac app we are developing unfortunately requires admin privileges to perform an occasional operation, and it also requires a background task to be live for other apps' plugins to connect to even when the app itself isn't running (this one can be unprivileged). The app will be signed with a Developer ID certificate, and distributed only outside the App Store.
We'd like the app to be a "good citizen" as far as possible, also on uninstall.
For the background task, we're using a login item, created using SMLoginItemSetEnabled(). This isn't amazing, because XPC messaging doesn't seem to work (we're using CFMessagePort instead - alternative suggestions welcome), but if the user deletes the app, the login item at least doesn't get loaded anymore on next login. I suspect there's still a trace of it somewhere in the system, but the executable inside the .app bundle is used, and when that disappears, the login item no longer runs.
For the occasional operation requiring admin rights, we've got a privileged helper tool which our app installs using SMJobBless(), and which implements a named XPC service, so the task spins up on demand when it receives a message from the main app. This is what Apple recommends and describes in its Even Better Authorization Sample.
The helper executable is copied to /Library/PrivilegedHelperTools/ by SMJobBless(), and the embedded launchd.plist ends up in /Library/LaunchDaemons/. Even though the OS has the information on which app "owns" the helper, it doesn't seem to uninstall it when the user deletes the app. Apple's sample is silent on uninstalling, other than the uninstall.sh script which is apparently intended to be used during development only. We don't need this helper while the app isn't running, so installing it as a full-blown launch daemon is slightly overkill, but we'd also like to avoid repeatedly annoying the user with the password prompt too. Besides, Apple advises against other forms of running code with admin privileges than SMJobBless() these days - for example SMJobSubmit() is marked deprecated.
So how do we clean up after ourselves?
I've found SMJobRemove(), but (a) when would we call that in our case - you can't run code on .app bundle deletion, or can you? and (b) it doesn't actually seem to clean up.
The only 2 things I can think of are not terribly satisfying:
There have been some changes in this area with macOS 13.0 Ventura; there's an introduction to the new mechanism in the WWDC22 session 'What’s new in privacy'. The new SMAppService APIs support automatic cleanup for daemons, agents and login items. Unfortunately you'll of course still have to find a workaround for any older macOS versions you support.
There has been a similar question on the Apple Developer Forums at https://forums.developer.apple.com/thread/66821 - the recommendation by Apple is a manual uninstall mechanism, and consuming as few resources as possible if the user does not do this.
Apple DTS staff further recommended implementing a self-uninstall mechanism in the privileged launch daemon, to be triggered from the app via XPC. This is what we're going with.