Agents that remember, pay,
and coordinate.

#[contract]
pub struct BudgetGuardrail;

#[contractimpl]
impl BudgetGuardrail {
  pub fn validate_payment(
    env: Env,
    agent_id: Symbol,
    amount: i128,
  ) -> Result<(), Error> {
    let spent = env.storage()
      .get::<Symbol, i128>(&agent_id)
      .unwrap_or(0);
    let cap = env.storage()
      .get::<Symbol, i128>(&symbol!("cap"))
      .unwrap_or(0);

    if spent + amount > cap {
      return Err(Error::BudgetExceeded);
    }
    env.storage().set(&agent_id, &(spent + amount));
    Ok(())
  }
}

#[contractimpl]
impl CounterpartyWhitelist {
  pub fn is_allowed(
    env: Env,
    destination: Address,
  ) -> bool {
    let whitelist: Vec<Address> = env
      .storage()
      .get(&symbol!("whitelist"))
      .unwrap_or_default();

    whitelist.contains(&destination)
  }

  pub fn add_address(
    env: Env,
    admin: Address,
    destination: Address,
  ) {
    admin.require_auth();
    // append to whitelist...
  }
}