AI agents fail differently from traditional software. A broken REST call throws an exception and halts. An agent calling the wrong tool with plausible-looking parameters might complete successfully, log no errors, and propagate a bad decision through three more steps before anything looks wrong. By the time a user notices, the trace is cold and the context window is gone.
This is the problem that's driving a new category of tooling. Traditional application performance monitoring was built around latency, error rates, and throughput. Those metrics matter for agents too, but they tell you almost nothing about whether the agent made the right call, picked the right tool, respected policy constraints, or hallucinated a result that downstream logic treated as ground truth. Observing an agent means capturing spans at the model-trace level, not just the HTTP level.
