The most common debug nightmare in multi-agent systems is 'the answer is wrong, but I don't know which agent did it.' Three layers of observability are essential: per-agent token metering, execution traces, and real-time cost dashboards.
LangSmith structures LLM applications as projects, traces, runs, and threads, then uses datasets, evaluators, and experiments to turn production failures into offline regression tests. It observes any LLM application and does not require LangChain.
Agentic Engineering isn't about making AI write code faster — it's about making software move through the entire delivery pipeline faster, by using multi-agent collaboration to compress cross-team coordination friction.
Rolling your own traces is good enough, but open-source tools save you a lot of work. Langfuse, Phoenix, and LangSmith each have their niche — the right choice depends on your trade-offs around self-hosting, open source, and integration complexity.