Observability pillars — traces, tool calls, decisions, failures

Theory . Why standard monitoring is insufficient for agents, which build their
own path at runtime rather than following fixed code. Students learn the pillars of
agent observability — execution traces, tool calls, decision steps, and failures — and
why you must read an agent's process, not just its final output.

Use cases . A support agent that returns a confident wrong answer and the
trace reveals it called the wrong tool; a coding agent whose final diff looks fine but
whose trace shows it never ran the tests; cost spikes traced to a single runaway
sub-agent. Each shows why the process, not just the output, is the unit of analysis.

Practical exercises .

• Concept-check: given a short annotated agent transcript, label each step as a
  trace event, tool call, decision, or failure, and identify where it first went wrong.
• Applied: turn on tracing for a provided sample agent, run one task, and read the
  resulting trace to narrate, in your own words, the path the agent actually took.