A LaunchAgent that had run for weeks began dying the moment it spawned, right after I shipped a rebuilt binary to the same path. The plist was untouched. codesign --verify passed on the new binary. launchd killed the job anyway.
The cause: launchd does not re-evaluate a job's code signature just because the file changed on disk. The verdict it formed when the job was registered stays attached to the registration. Replace the binary and the job carries the stale verdict until the registration itself is rebuilt.
So the fix is to tear down and re-register the job, not to re-sign or re-copy the binary:
launchctl bootout gui/$UID ~/Library/LaunchAgents/com.example.worker.plist
launchctl bootstrap gui/$UID ~/Library/LaunchAgents/com.example.worker.plistlaunchctl kickstart -k only restarts the process; it inherits the cached verdict. bootout plus bootstrap forces a fresh evaluation.