# LST Architecture

Endur's liquid staking system employs a three-component architecture:

### **a) LST Contract (Main Contract)**

* Implementation: ERC-4626 vault contract
* Manages deposits and withdrawal requests
* Primary interface for users interacting with the system

### **b) Withdraw Queue Contract**

* Issues unique NFTs for withdrawal requests
* Each NFT represents:
  * Amount of STRK/BTC requested for withdrawal
  * Timestamp of request
  * Position in the queue
* Manages the orderly processing of withdrawals (first come, first serve)
* Fund settlement sources ([learn more here](https://docs.endur.fi/docs/concepts/deposit-withdraw-matching)):
  1. New deposits (prioritized for pending withdrawals)
  2. Unstaked funds from delegators

### **c) Delegator System**

* Multiple delegator contracts manage actual staking with Starknet
* The system acts as an intermediary between the LST system and Starknet's staking system
* It handles the actual staking operations.
* Here's how the fund flows:
  1. Excess funds from LST → Delegators -> stake STRK/BTC
  2. When withdrawing: Unstaked funds -> Withdraw Queue

### **d) Validator registry**

* Responsible for whitelisting validators, supported tokens and delegators
* Handles stake/unstake/restaking rewards

### **e) Swap Extension**

* Responsible for temporarily holding STRK rewards to swap to respective BTC tokens. Not applicable for xSTRK. Receives rewards from delegator, swaps and sends to Validator registry which can be re-staked again. 

### **Flow chart of interactions:**

<figure><img src="/files/htblSbbdezWgaMFgIh7u" alt=""><figcaption></figcaption></figure>

#### Deposit Flow:

1. User deposits STRK/BTC to LST Contract
2. System checks withdrawal queue demands
3. Excess funds distributed to delegators
4. Delegators stake on Starknet

#### Withdrawal Flow:

1. User requests withdrawal
2. NFT issued to user
3. Protocol either:
   * Matches with available funds
   * OR initiates unstaking through delegators
4. Funds released according to queue position

This architecture ensures:

* Efficient capital utilisation
* Efficient unstaking time through multiple delegators
* Transparent withdrawal process as you can see in withdraw log
* Automated reward distribution
* Failsafe withdrawal mechanisms


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