How do I tell Xamarin to open a file to a line in an open Xamarin instance?

I'm using an outside program to send a shell command to Xamarin to open a file. What this does is it opens a second copy of Xamarin, and that copy of Xamarin opens the file regardless of whether the file is already open in a tab.

I need to use the same instance of Xamarin, and I need to use the existing open file if one exists.

Worst-case scenario, I can write a quick thing to close the existing Xamarin and just reopen a new one (oh god the loading times!), but I still don't know how to prevent Xamarin from double-opening the file.

Are there any settings I can tweak? If these changes require source changes, you'll have to treat me like a baby; I know C# but I don't know how Xamarin's source is arranged.