D1. JSON Schema 2020-12 is the source of truth

The format is a published spec, read by tools in other languages (Python import tools, third-party agents, LESSON.md converters). JSON Schema is the language-neutral standard that MCP and every model API consume; x-* annotations drive generated editors; cross-field rules (plan coverage, references) live in the validator with stable codes, so Zod refinements would add nothing that survives export. Schemas are kept simple for model decoders: flat objects, type discriminators, enums, descriptions on every field. Revisit if: the editor team wants typed authoring in TypeScript — use TypeBox or generated types, not a second source.