How do you actually know your AI agent did what it says it did?

Something that bugs me the more I build with agents. An agent runs, does a bunch of stuff you didn't watch, and hands you a summary. You get a confident paragraph saying it analyzed the data and here's the recommendation. And… you kind of just believe it? There's no way to check which model actually ran, what it actually looked at, or whether it did the work at all versus generating something that sounds like it did. For a writing assistant, who cares. But people are handing agents real jobs now like moving money, sending messages, making decisions that are annoying to undo. At that point "trust me, I did it" is a weird place to land. What I keep wanting is a receipt. Not a log the agent writes about itself, which is just the same trust problem one level down, but something the agent can't fake: which model ran, what went in, what came out, verifiable by someone who wasn't there. Worth saying, a receipt doesn't mean the agent was right. A model can be verifiably run and still be badly wrong. It just means you can tell the difference between a bad decision and a decision that never happened. How are you all handling this? Logging everything and hoping?