Function validate_document_shape 

pub fn validate_document_shape(
    document: &Document,
) -> Result<(), DocumentShapeError>

Validate the enumerated structural snapshot strict document operations rely on.

This is a snapshot only: Document is publicly mutable, so a successful call does not certify a document against later mutation. Any strict operation that relies on this full shape must rerun validation at its own public boundary. Tolerant analysis APIs may intentionally accept documents this rejects and preserve the valid evidence they can read. This function does not validate operation-specific capability, affine, closure, proof, or payload invariants such as primitive skinning shape and base positions.

Errors

Returns a typed DocumentShapeError for the first violation in stable validation order: skeleton rest/topology, source identity/projection, tracks, instances, then bone-level inverse binds.