Function rewrap_passphrase_custody 

pub fn rewrap_passphrase_custody(
    store_dir: &StoreDir,
    old: Passphrase,
    new: &Passphrase,
) -> Result<(), KeyError>

Re-wrap a store’s passphrase-protected master keyring under a new passphrase — the store-side half of covenpass’s “change passphrase”. The <store_dir>/master.keyring envelope is decrypted with old and re-sealed under new (fresh salt and nonce). Errors if nothing is established there (KeyError::Persistence) or if old is wrong (KeyError::Crypto), leaving the existing file untouched on either failure. After it returns, the store’s custody is re-opened under new.