Assistive Access when script is launched by agent
A simple fix is to save the script as a text file instead.

At the top of the script add the osascript shebang

#!/usr/bin/osascript

example:

#!/usr/bin/osascript
say "hello"
tell application "Safari" to activate
tell application "System Events"

    delay 2
    keystroke "p" using command down
    tell application process "Safari"

        tell application "System Events"
            tell process "Safari"
                click menu button "PDF" of sheet 1 of window 1
                delay 1

                click menu item "Save PDF to Web Receipts Folder" of menu of menu button "PDF" of sheet 1 of window 1
            end tell
        end tell
    end tell

end tell


The in the save dialog choose Text as the file format.
The file will be saved as plain text but with the .applescript extension.

In terminal make the save script text file executable.

I used:

chmod +x /Users/UserName/Scripts/newTest1.applescript

In the command arguments of the LaunchAgent just add the path to the file.

Do not add the osascript command to the arguments. You do not need it.

The saved script text file will act like an executable shell script.

When you first load or run the LaunchAgents you will get a prompt to set the  Assistive Access in System Preferences. If you already have System preferences open you will not but the Script text file will be added to the list.

You now just have to check its check box to allow it.

I would reload the LaunchAgent so it picks up straight away.

I have double checked this with the script above and all works as expected.