Pattern
The Trace Is The Truth
If you can't inspect why the agent did what it did, you can't debug, audit, or improve it.
When to use
Always. Tracing is a first-class system requirement, not a nice-to-have. Every tool call, every reasoning step, every retry should be inspectable in a structured log.
When not to use
Never. The only valid reason to skip tracing is "prototype, will throw away" — and prototypes that survive contact with users always become production.