Strict, schema-driven loading of definition JSON. Each definition is deserialized directly into a well-typed object via System.Text.Json with full F# support (records, options, unions, lists, maps). The schema is described once by the `*Wire` records below; anything that does not match it — a wrong type, an unknown union tag, an unknown property, or a missing required field — throws instead of being silently defaulted. There are no aliases and no value fallbacks: omission is the ONLY leniency, and only for fields modelled as `option`, which then resolve to their type's natural empty value.