## Why
The npm wrapper can exit successfully after its native child is terminated by a signal if Node ignores the re-emitted signal or a forwarding handler intercepts it.
## What changed
Set a fallback exit status of `128 + signal number` and remove listeners for the terminating signal before re-emitting it, preserving signal termination where supported.
## Testing
Add a non-Windows integration test using a built Codex binary to cover numeric argument-error exits, forwarded `SIGHUP` termination, and the fallback exit status for `SIGXFSZ`, which Node ignores by default.
GitOrigin-RevId: cad18a47aa50fd78517c367f8d8aae83bbbf7843
