structured output

Tool calling passes through four layers and a break in any one produces the same symptom, so the debugging is a bisection rather than an investigation. Which layer the size of the drop points at, the deploy diff that usually contains the answer, and why no latency metric moved.

Prompting for JSON produces valid JSON most of the time, and most of the time is not a contract. Constrained decoding makes it a guarantee by restricting what the sampler may choose, and the cost is a compilation step and a throughput effect that depends entirely on how complex the schema is.