the same thing almost happened to me in an old barn outside of Omaha, except it was a root cellar door that slammed shut on its own. i had my phone but no service, so i just sat there for like two hours until my cousin realized i was gone and came looking. what worked for me after that was always carrying a small multi-tool with a screwdriver attachment, and i started wedging a piece of wood or a rock in any door or hatch before i go in. honestly, the scariest part is how quiet it gets, and how your mind starts spinning on worst case scenarios. glad your buddy came through, but maybe invest in a cheap emergency whistle to keep on your keychain, cause that carries further than yelling. idk if it helps, but now i treat any old structure like it's trying to trap me, and that keeps me from being careless.

OH wow, that timing thing is HUGE. But here's the part nobody talks about: your fridge's temp swings make a difference too. Instead of letting it sit at a steady 38 degrees, I started putting my dough on the TOP shelf where it's colder, and the bottom shelf is warmer in most fridges. That little temp change during the 48 hours does something to the yeast activity that you just CAN'T replicate on the counter. Try moving your dough around halfway through, it really wakes up the gluten in a weird way. Also, don't forget to let that cold dough sit out for like 30 minutes before you shape it, otherwise you're fighting a brick. Your crust crack probably came from the cold slowing down the outer skin while the inside still had steam going. That's my two cents anyway, enjoy the better bread!