Citadel Vault

Endur xWBTC liquid staking + Vesu lending for dual yield

Sable Citadel

The Citadel vault combines Endur liquid staking with Vesu lending to generate dual yield streams on deposited WBTC.

Risk Level: 2 (Low-Medium)
Strategy: Stake WBTC → xWBTC → Supply to Vesu as collateral

Strategy Overview

WBTC → Endur Vault → xWBTC (liquid staking token)
                        ↓
                   Vesu Re7 xBTC Pool (collateral)
                        ↓
         Dual Yield: Staking APY + Lending APY + STRK Rewards

Yield Sources

Source	Type	Description
Endur Staking APY	Base yield	Validator rewards from BTC staking via Endur
Vesu Lending APY	Additional yield	Interest from xWBTC lending on Vesu
BTCFi STRK Rewards	Incentive	100M STRK distribution
xWBTC Appreciation	Capital gain	xWBTC/WBTC ratio increases over time

Risk Profile

• No leverage: No borrowed positions or liquidation risk
• Endur protocol risk: Smart contract and liquid staking risks
• 7-day withdrawal queue: Endur unstaking takes 7 days (mitigated by AVNU swap)
• xWBTC/WBTC depeg risk: Minimal due to Endur’s backing mechanism

---

Contract Architecture

File: citadel.cairo (~600 LOC)
Deployed: 0x077ad8d0fe4b946cedc02eb8eb61a64e85bcde802a83e879e8c68fed8b9b130e

Core Components

Dual Strategy

Citadel manages two distinct positions:

1. Endur xWBTC: Liquid staking shares (ERC-4626)
2. Vesu Collateral: xWBTC supplied to Vesu Re7 xBTC pool

struct Storage {
    // ...
    endur_vault: ContractAddress,     // Endur xWBTC ERC-4626 vault
    vesu_singleton: ContractAddress,
    vesu_pool_id: felt252,
    // Strategy state
    xwbtc_staked: u256,               // Total xWBTC shares held
    vesu_collateral: u256,            // xWBTC supplied to Vesu
    is_paused: bool,
}

Endur Integration

Citadel stakes WBTC into Endur’s ERC-4626 vault:

fn stake_to_endur(ref self: ContractState, amount: u256) {
    self._assert_owner();
    let wbtc = IERC20Dispatcher { contract_address: wbtc_addr };
    wbtc.approve(endur_addr, amount);

    // Deposit WBTC → receive xWBTC shares
    let endur = IERC4626Dispatcher { contract_address: endur_addr };
    let xwbtc_shares = endur.deposit(amount, this);

    self.xwbtc_staked.write(self.xwbtc_staked.read() + xwbtc_shares);
    self.emit(EndurStake { wbtc_in: amount, xwbtc_out: xwbtc_shares });
}

From citadel.cairo:327

Vesu Integration

Citadel supplies xWBTC to Vesu Re7 xBTC pool as collateral:

fn deploy_xwbtc_to_vesu(ref self: ContractState, amount: u256) {
    self._assert_owner();
    let xwbtc = IERC20Dispatcher { contract_address: endur_addr };
    xwbtc.approve(pool_addr, amount);

    let params = ModifyPositionParams {
        collateral_asset: endur_addr,  // xWBTC
        debt_asset: wbtc_addr,         // Registered asset (no debt)
        user: this,
        collateral: Amount {
            denomination: AmountDenomination::Assets,
            value: i257 { abs: amount, is_negative: false },
        },
        debt: Amount { /* ... zero debt ... */ },
    };
    vesu.modify_position(params);
}

From citadel.cairo:347

---

Key Functions

User Functions

deposit · function

Deposit WBTC and receive yvBTC-CIT shares

Parameters:

• assets (u256): Amount of WBTC to deposit (8 decimals)
• receiver (ContractAddress): Address to receive vault shares

Returns: u256 — Number of shares minted

Auto-deploys to: WBTC → Endur → xWBTC → Vesu collateral

withdraw · function

Burn shares and withdraw WBTC

Parameters:

• assets (u256): Amount of WBTC to withdraw
• receiver (ContractAddress): Address to receive WBTC
• owner (ContractAddress): Share owner

Returns: u256 — Number of shares burned

Auto-unwind: Withdrawals trigger:

1. Withdraw xWBTC from Vesu
2. Swap xWBTC → WBTC via AVNU (Ekubo pool)
3. Transfer WBTC to receiver

Curator Functions

stake_to_endur · function

Stake idle WBTC into Endur vault

Parameters:

• amount (u256): WBTC to stake

fn stake_to_endur(ref self: ContractState, amount: u256)

Implementation at citadel.cairo:327

deploy_xwbtc_to_vesu · function

Supply xWBTC to Vesu Re7 xBTC pool

Parameters:

• amount (u256): xWBTC shares to supply

fn deploy_xwbtc_to_vesu(ref self: ContractState, amount: u256)

Implementation at citadel.cairo:347

withdraw_from_vesu · function

Withdraw xWBTC collateral from Vesu

Parameters:

• amount (u256): xWBTC shares to withdraw

fn withdraw_from_vesu(ref self: ContractState, amount: u256)

Implementation at citadel.cairo:382

unwind_xwbtc · function

Emergency unwind: withdraw all xWBTC from Vesu + swap to WBTC via AVNU

Parameters:

• min_amount_out (u256): Minimum WBTC output (slippage protection)
• routes (Array<Route>): AVNU swap routes

fn unwind_xwbtc(ref self: ContractState, min_amount_out: u256, routes: Array<Route>)

Implementation at citadel.cairo:429

Uses AVNU to bypass Endur’s 7-day withdrawal queue.

---

Integration with External Protocols

Endur Liquid Staking

Vault Address: endur_vault (constructor parameter)

Citadel uses Endur’s ERC-4626 vault to stake WBTC:

let endur = IERC4626Dispatcher { contract_address: endur_addr };
let xwbtc_shares = endur.deposit(wbtc_amount, vault_address);

xWBTC Share Price: Increases over time as staking rewards accrue

Vesu Re7 xBTC Pool

Pool ID: 0x03a8416bf20d036df5b1cf3447630a2e1cb04685f6b0c3a70ed7fb1473548ecf

Citadel supplies xWBTC as collateral (no debt) to earn BTCFi rewards:

let params = ModifyPositionParams {
    collateral_asset: endur_addr,  // xWBTC token
    debt_asset: wbtc_addr,         // Valid asset (zero debt)
    user: vault_address,
    collateral: Amount { /* xWBTC shares */ },
    debt: Amount { /* zero */ },
};
vesu.modify_position(params);

AVNU xWBTC/WBTC Swap

For withdrawals, Citadel swaps xWBTC → WBTC via Ekubo xWBTC/WBTC pool (fee: 0.01%, tick_spacing: 200):

let swap_params: Array<felt252> = array![
    wbtc_felt,    // token0 (WBTC < xWBTC by address)
    endur_felt,   // token1
    0x68db8bac710cb4000000000000000, // fee
    0xc8,         // tick_spacing = 200
    0x0,          // extension
    0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF, // sqrt_ratio_limit (max)
];

From citadel.cairo:697

---

Example Usage

Depositing WBTC

import { Contract } from 'starknet'

const citadelVault = new Contract(citadelABI, citadelAddress, account)
const wbtc = new Contract(erc20ABI, wbtcAddress, account)

// 1. Approve vault
const amount = 50_000_000n // 0.5 WBTC
await wbtc.approve(citadelAddress, amount)

// 2. Deposit (auto-stakes to Endur + supplies to Vesu)
await citadelVault.deposit(amount, account.address)

// 3. Check yvBTC-CIT balance
const shares = await citadelVault.balance_of(account.address)

Withdrawing WBTC

// Get withdrawable assets
const maxWithdraw = await citadelVault.max_withdraw(account.address)

// Withdraw all (auto-unwinds xWBTC → WBTC swap)
await citadelVault.withdraw(maxWithdraw, account.address, account.address)

Checking Strategy State

// Total xWBTC staked (shares)
const xwbtcStaked = await citadelVault.get_endur_staked()

// xWBTC supplied to Vesu
const [vesuCollateral, debt, loops, paused] = await citadelVault.get_strategy_info()

// Convert xWBTC shares to WBTC value
const endurVault = new Contract(erc4626ABI, endurAddress, provider)
const wbtcValue = await endurVault.convert_to_assets(xwbtcStaked)

---

Security Considerations

Risks

1. Endur Protocol Risk: Smart contract vulnerabilities in Endur’s staking mechanism
2. xWBTC Depeg Risk: If Endur’s backing mechanism fails, xWBTC could trade below WBTC
3. Vesu Pool Risk: Smart contract risk in Vesu Re7 xBTC pool
4. Swap Liquidity Risk: Low liquidity in xWBTC/WBTC Ekubo pool could cause slippage on large withdrawals

Risk Mitigation

• 7-day queue bypass: AVNU swap allows instant withdrawals without waiting
• No liquidation risk: Citadel never borrows, so no liquidations
• Pause mechanism: Owner can halt deposits if issues arise
• Upgradeable: Contract can be upgraded to fix bugs

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Additional Resources

• Endur Documentation
• Vesu Documentation
• AVNU DEX Aggregator
• Source Code
• Voyager Explorer