When your agent screws up in production, how do you figure out which step went wrong?

Been building multi-step agents and the thing that's killing me isn't building them, it's knowing what happened when they fail. Like the agent works fine when I test it, then in real use it does something dumb — picks the wrong tool, or gives a confident wrong answer — and I'm stuck digging through logs trying to figure out which step in the chain actually went off the rails. Right now my "process" is honestly just print statements everywhere and re-reading the trace by hand. Feels primitive. How are you all handling this? * Do you have any real way to catch when an agent regresses after you change something? * For the people running agents in prod — how do you even know they're still working well day to day? * Anyone found something that actually helps here or is everyone just reading logs? Trying to figure out if I'm doing this the hard way or if there just isn't a good answer yet