Is there an existing issue for this?

• I have searched the existing issues

This issue exists in the latest npm version

• I am using the latest npm

Current Behavior

Any script which writes to standard output but does not emit a \n as its final character will have output erased when npm run exits.

Expected Behavior

npm run should never interfere with the output of scripts.

Steps To Reproduce

1. Create a package.json file like this:

   {
     "name": "",
     "version": "0.0.0",
     "scripts": {
       "start": "printf 'this output will vanish'; sleep 3"
     }
   }

2. Run npm run start.
3. Observe that the output vanishes after three seconds.

Environment

• npm -v: 11.6.0
• node -v: v22.18.0
• OS Name: macOS 15.6
• System Model Name: MacBook Pro
• npm config:

  //localhost:4873/:_authToken = (protected)
  //registry.npmjs.org/:_authToken = (protected)