I'm tired of manually debugging traces

I feel like there's been a lot of posts lately about agents that work once, then do something different the next time. Different tool call, different args, weird branch, loop, state issue, etc. The trace/log exists, but you still end up manually trying to figure out where the behavior actually changed. We ran into this in some of our own agent projects too, so me and my friend started building a debugging tool for our own sake. The idea is simple: compare a replay against a reference run and show the first place it drifted. Interested about how people are efficiently debugging this today. LangSmith/Langfuse, evals, custom logs, manual trace comparison, or something else?