Shoutbox

So, you don't want the current user who clicked on that link to send the message, but receive a message in a chat window, right?

But then...

• ...who would send that message?
  
• ...why can't you just display a toast when the user clicks that link, and make the site open when the user clicks the toast?
  
• ...why can't you just make a link do what a link is supposed to do: open a web page?

I think your logic simply doesn't work.

By the way, it's not possible that you see a message in a chat window without having your contact see it too, whether that contact sent or received that message!