Function add_grouped_secret 

pub fn add_grouped_secret(
    vault: &mut Vault,
    murk: &mut Murk,
    key: &str,
    value: &str,
    desc: Option<&str>,
    group: &str,
    tags: &[String],
    operator_pubkey: &str,
) -> Result<bool, MurkError>

Add or update a secret encrypted to a named group. The operator must be a member of the group (so they can read it and re-encrypt it later). Assigning a secret to a group makes the group its sole base tier: any existing shared value and other group assignments are dropped so non-members can’t read it. Returns true if the key was new (no existing schema entry).