I've tried adding everything I can think of to "System Preferences / Security / Privacy / Accessibility" including osascript, cron, launchd and System Events.
E.g., osascript -e 'tell application "System Events" to key code 100'
The only maybe-relevant thing I can see in the relentless firehose that is the system log is: "spawn_via_launchd() failed, errno=1 label=[0x0-0x566566].com.apple.systemevents path=/System/Library/CoreServices/System Events.app/Contents/MacOS/System Events flags=0"
Remember when programs fought for the users instead of against them? Yeah, neither do I.