So here's the closest thing to signposts that I've found. Bernstein writes that the delegates and the candidates will run the convention. The candidates are pretty well known by now, but what about the delegates? Who are they, who are they loyal (or disloyal) to, and what will their motivations be? Perhaps Cruz has enough on-the-ground infrastructure to ensure that his delegates are loyal, but can Trump? I can't even guess.
Another possibility (likely is my gut feeling) is that Trump and Cruz together will control the convention. Any establishment hopes for avoiding Awful#1 and Awful#2 will be dashed. My guess is that Cruz will be offered and will accept the nomination for vice-president. I didn't think of this myself, but once I read it, it seems absolutely perfect. They've been buddies before. They can go back to being buddies with all smears forgotten in mists of amnesia. They will share their hatred of the RINO, lying, feckless establishment, and their absolute certainty of victory... If I watch, I'll want to puke.
To avoid puking, I'd like to pretend that the GOP establishment and good sense will prevent this. But looking at the disarray in the GOP leadership, I can't imagine it will happen. It's quite hopeless. We'll be looking at a convention and a general campaign without precedent in my lifetime. So hold on tight.
Extra. Read about the 1976 GOP convention, which was contested. Ford was ahead of Reagan, but neither had a lock. Nonetheless, there were clear signals early that Ford would win.