Preserve child signal failures in the npm wrapper (#57352)

## 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

codex-cli/bin/codex.js

@@ -4,6 +4,7 @@
 import { spawn } from "node:child_process";
 import { existsSync, readFileSync, realpathSync } from "fs";
 import { createRequire } from "node:module";
+import { constants } from "node:os";
 import path from "path";
 import { fileURLToPath } from "url";
 
@@ -287,8 +288,9 @@ const childResult = await new Promise((resolve) => {
 });
 
 if (childResult.type === "signal") {
-  // Re-emit the same signal so that the parent terminates with the expected
-  // semantics (this also sets the correct exit code of 128 + n).
+  // Preserve a failure exit code even if Node ignores the re-emitted signal.
+  process.exitCode = 128 + constants.signals[childResult.signal];
+  process.removeAllListeners(childResult.signal);
   process.kill(process.pid, childResult.signal);
 } else {
   process.exit(childResult.exitCode);