validation

Each layer depends on the ones below it and a mistake at the bottom shows up six layers higher as something else entirely. The order, the dependency almost everyone gets wrong on Blackwell systems, and the validation ladder that keeps a fault attributable to one node instead of five hundred.

Acceptance is a contract document, not a checklist, so every criterion has to be a number with a tolerance that a vendor can be held to. Comparing nodes against each other rather than against a datasheet is what finds real defects, and the duration is what finds the thermal ones.

A check that is too strict removes healthy capacity and one that is too loose lets a broken node take a job down. The three tiers by cost, the fleet-median comparison that catches degradation no threshold does, and the false-positive budget that has to be set before any of it runs.

Two steps consume most of the week and neither is the one people plan for. The gate that can end the project on day one, the multi-hour download, the correctness check almost nobody runs, and the canary that has to see real traffic before Friday.

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.

Three tools measure three different things, and a link can pass one while failing another. The message-size sweep that separates a latency problem from a bandwidth problem, the number each test should return on a healthy 400 gigabit port, and the single test that catches the failure the others miss.

Three decisions decide whether this is correct: the numeric type, how partial hours are handled, and what happens to a record that does not make sense. The implementation with its tests, the floating-point trap that costs real money, and the questions to ask before writing any of it.