Vault Share Token (nVault)

#[contract]
pub struct VaultToken;

#[contractimpl]
impl VaultToken {
    pub fn initialize(env: Env, admin: Address, name: String, symbol: String, decimals: u32);

    /// Mint shares to user (called by vault on deposit)
    pub fn mint(env: Env, to: Address, amount: i128) {
        Self::require_vault_caller(&env);  // Only vault contract can mint
        // ... mint logic
    }

    /// Burn shares from user (called by vault on withdraw)
    pub fn burn(env: Env, from: Address, amount: i128) {
        Self::require_vault_caller(&env);
        // ... burn logic
    }

    // Standard SEP-41 token interface
    pub fn balance(env: Env, id: Address) -> i128;
    pub fn transfer(env: Env, from: Address, to: Address, amount: i128);
    pub fn allowance(env: Env, from: Address, spender: Address) -> i128;
    pub fn approve(env: Env, from: Address, spender: Address, amount: i128);
    pub fn total_supply(env: Env) -> i128;
    pub fn name(env: Env) -> String;
    pub fn symbol(env: Env) -> String;
    pub fn decimals(env: Env) -> u32;
}

nDEFI token value tracks:
  Top 5 DeFi protocols by risk-adjusted yield
  Monthly rebalance adjusts weights
  User holds 1 token = exposure to entire index