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The most brute force method to deal with this would be to add a listener for the copy event and modify the copied text to remove lines and other formatting that you consider extra. 

```js
document.addEventListener('copy', function(e){
  // Get the copied text
  const text = window.getSelection().toString();

  // Do some modification
  const cleanedCopy = doSomeProcessing(text);

  // Change the clipboard data.
  e.clipboardData.setData('text/plain', cleanedCopy);
  e.preventDefault();
});
```

In your case I think you do not want the double new lines in the copied text. This would be a very rough fix as it would remove any legitimate double newlines as well. And doesn't account for copying images, etc. 
```
document.addEventListener('copy', function(e){
  const text = window.getSelection().toString();
  // Change all double newlines whether on windows or unix to just one newline.
  e.clipboardData.setData('text/plain', text.replaceAll(`\n\n`, `\n`).replaceAll(`\r\n\r\n`, `\r\n`));
  e.preventDefault();
});
```