Revert Signal Handling Regression

[wiktor-obrebski]

Description

This PR reverts the changes made in commit 545f3be94d412941537ad0011717933d48cb58cf, which inadvertently broke signal forwarding to child processes (PR #142 ).
Contrary to the assumptions by @nlf , SIGTERM and similar signals are not being correctly propagated to child processes. Instead, they are only received by npm, resulting in incomplete signal handling.

The removal of signal forwarding in #142 means that child processes do not receive necessary signals for appropriate cleanup and termination.

This issue is evident in workflows involving npm start used as a Docker command for local execution. For instance, using CTRL + C does not properly terminate the application
and results in a forced kill after a 10-second delay.

This behavior could lead to more significant problems in production environments, (if npm is used to start the app) such as data loss due to improper database connection closures.

Minimal Reproduction Steps

Create a package.json with the following content:

{
  "name": "npm",
  "scripts": {
    "start": "node ./main-test.js"
  }
}

Create a main-test.js file:

const interval = setInterval(() => console.log('alive!'), 3000);

async function onSignal(signal) {
  console.log(`${signal} received, cleaning up...`);
  clearInterval(interval);
  console.log('Cleaning up done');
}
process.on('SIGINT', onSignal);
process.on('SIGTERM', onSignal);

Execute npm start. The script should output alive! every 3 seconds.
Attempt to terminate it using kill -SIGTERM [PID].
It should log Cleaning up done and shut down gracefully,
which it does in older versions of npm (e.g., v8.19.4) but fails in newer versions (e.g., v9.6.7).

Impact

Reverting this change will restore the expected behavior for signal handling in npm

References

• [BUG] npm >= 9.6.7 does not pass signals to the running script cli#6547
• [BUG] npm not handling process signals cli#6684
• fix: handle signals more correctly #142

[bencripps]

This seems like a pretty critical issue; it's breaking the graceful shutdown behavior of a lot of our applications; could we get this merged ASAP?