Pluggable JSON Schema Validation

The built-in jsonSchema check (checkJsonSchema) is intentionally shallow - it validates type, enum membership, and required presence (recursing through properties/items), but not minLength/maximum/pattern/oneOf/$ref/etc. Rather than expanding it, it's pluggable: supply your own validator (or wire up AJV) via jsonSchemaValidator.

const strictValidator = (value: unknown, schema: Record<string, unknown>) => {
  // throw to reject; return normally to accept
  const v = value as { age?: number };
  if (typeof v.age !== "number" || v.age < 0 || v.age > 130) {
    throw new Error("age must be a plausible human age");
  }
};

const result = await generate(model, { jsonSchema: PersonJsonSchema }, prompt, {
  jsonSchemaValidator: strictValidator,
});

Applies to both generate()'s final check and generateStream()'s per-field incremental (partial) validation, so a custom validator behaves consistently whether or not you're streaming. Omit it and you get today's checkJsonSchema behavior, unchanged.