Forward repeated signals through the npm wrapper (#61221)

## Why

The npm wrapper's spawn fallback stopped forwarding signals after the first one, preventing a second signal from interrupting a child's graceful shutdown.

## What changed

Remove the `child.killed` guard so the wrapper continues forwarding `SIGINT`, `SIGTERM`, and `SIGHUP` until the child exits.

## Testing

Add a regression test that forces the spawn fallback and verifies a running child receives a second `SIGTERM` and its numeric exit status is preserved.

GitOrigin-RevId: be96e784e2e4f419c43a5897d264f55fcdfd625f

codex-cli/bin/codex.js

@@ -258,14 +258,9 @@ child.on("error", (err) => {
   process.exit(1);
 });
 
-// Forward common termination signals to the child so that it shuts down
-// gracefully. In the handler we temporarily disable the default behavior of
-// exiting immediately; once the child has been signaled we simply wait for
-// its exit event which will in turn terminate the parent (see below).
+// Keep forwarding signals until the child exits so a second signal can
+// interrupt a graceful shutdown.
 const forwardSignal = (signal) => {
-  if (child.killed) {
-    return;
-  }
   try {
     child.kill(signal);
   } catch {