Function sanitize_structural_continuation_metadata 

pub fn sanitize_structural_continuation_metadata(
    bytes: &[u8],
    semantic_is_safe: impl FnOnce(u16, &[u8]) -> bool,
) -> Option<Vec<u8>>

Validate and canonicalize a framework envelope at the shell boundary. An unrecognized app projection is removed rather than retained as opaque bytes; its generic presentation checkpoint remains usable on every device.