Function open_sealed_blob 

pub fn open_sealed_blob(
    stored: &[u8],
    encryption: &EncryptionService,
    aad_context: &[u8],
) -> Result<(KeyFingerprint, Vec<u8>), EncryptionError>

Open a blob this layer sealed: split the prefix, then open every chunk under encryption with the AAD context the seal was bound to. Returns the fingerprint of the key that sealed it alongside the plaintext.