Long uphill grunt and just before the third lookout my shifting completely goes to h*ll. Clanking and grinding, I bail to take a look and the rear derailleur is wedged into the cassette! Turns out my DT Swiss rear axle has come unscrewed, so I'm screwed. I walked back down a bit, upended the bike and screwed it back in and rode down. Tightened everything when I got home, glad it didn't happen while descending. Olallie is dry and running well!