Per the Changelog at https://www.php.net/manual/en/function.exit.php, since PHP 8.4.0, "exit() is now a proper function, therefore it follows the usual type juggling semantics is affected by the strict_types declare".
ERROR 8192: exit(): Passing null to parameter #1 ($status) of type string|int is deprecated at [/arcanist/src/parser/argument/PhutilArgumentParser.php:494]
Closes T15990