I can tell the launchd agent plist to delete itself by adding its full path and editing it every time for every tool, but is there a better way?
I am unaware of any
launchd .plist setting/command that will allow it to "delete itself."
When your Mac boots and when you load a .plist,
launchd scans (as applicable):
/System/Library/LaunchDaemons. If the .plist isn't there, it doesn't load.
So, if you "check to see if the tool exists and remove itself" you'll need to incorporate that logic as part of the script that's kicked off by launchd.
Is there (for example) a variable I could grab where the launchd returns its own name or path?
launchd doesn't return "its own name or path;" it loads/unloads/launches/stops a job defined by a .plist at a path. Therefore, if you want that variable to be available, you'll need to set it as part of the environment defined in the .plist.
That said, I don't believe it possible that you can both have a job running and simultaneously unload it especially by itself; more so if it requires elevated privileges to do so. This is probably why install/uninstall requires user intervention.
Additionally, per the man page for
launchd.plist it addresses agents/daemons accessing "protected" files/folders:
Daemons and agents managed by launchd are subject to macOS user privacy protections. Specifying privacy sensitive files and folders in a launchd plist may not have the desired effect, and may prevent the job from running.
By having an agent call a script that in effect deletes itself (from one of the directories listed above) may have unintended consequences and may not even run.