A web API fails loudly: a 500, a stack trace, an alert. An agent fails softly. It doesn't crash — it quietly takes six turns instead of two, calls the wrong tool, spends triple the tokens, and returns an answer that's subtly wrong. None of that throws an exception, and none of it shows up in the logs of any single request.
This is Part 10 of a 15-part deep dive on Model Context Protocol (MCP). Part 3 gave each tool call a span on the server; this part joins those into the whole picture — one agent run across the host, the model, and all three servers, correlated so that when something feels off you have an answer instead of a shrug.
One agent run, as a trace
agent.run (tenant, goal) [==================] 1.8s
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