Emits each member of the public exit-code taxonomy so orchestrators can pattern-match on $? without parsing stderr. success=0, generic=1, policy_denied=2, upstream_failed=3, internal=4, user_error=5.
$ go run ./examples/exitcode success ; echo "exit: $?"
exit: 0
$ go run ./examples/exitcode policy ; echo "exit: $?"
argv rejected
exit: 2