Function load_file_header_bytes 

pub fn load_file_header_bytes(file: &ShadowFile) -> WorkflowResult<SecureBytes>

Reads enough leading bytes of a shadow file to cover its complete header, whatever its format version. Parsing happens in the workflow via shadow_crypt_core::vault::ParsedFile, which tolerates trailing ciphertext bytes, so no version-specific length probing is needed here.