I am totally making it my ringtone as soon as I can.

As for who Diane's texting (aside from the uppercase/lowercase difference in the text she received), in her reply, she started with, "They have Hastings." Would she bother telling Dirty Cooper what he already knows, if she's trying to text furtively in the brief moments she manages to get alone? He went to the trouble…

But did she give two rides?

I don't think it's established that she was responding to Evil Cooper. Why would she tell him they have Hastings, when he surely knows that, that was the point of framing him for the Ruth/Briggs murders? So the question is: who is it that doesn't know that Hastings is in custody?

I would follow your submarine blog.