The generated dict-to-struct conversions for nested records defaulted every
absent field and ignored unknown keys, so an LwPolyline built from
{'x': .., 'y': ..} vertices became zero-coordinate vertices. They now refuse an
unknown key (naming the keys the record takes) and a manifest list,
required_struct_fields, enforces the fields that define a nested record's
geometry (vertex locations, hatch edge ends and centres, section symbol points).
Regression test over real IPC; every existing lifecycle audit still passes.
Co-Authored-By: Claude Sonnet 5 <[email protected]>
