feat: implement Dutch auction liquidation interface with commit-reveal front-running protection (#746)

- Add auction-types shared library with Auction, AuctionConfig, BidCommitment, BidReveal, BidResult types
- Add liquidation-auction contract with full Dutch auction lifecycle
- Support linear and exponential price decay functions
- Configurable starting premium, floor discount, and auction duration
- Partial fills with commit-reveal scheme for MEV protection
- Auction cancellation when position health is restored
- Event emissions for all auction lifecycle events (start, bid, settle, cancel)
- Add both contracts to workspace Cargo.toml

Closes #446

Author: Junman140

stellar-lend/contracts/auction-types/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "auction-types"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+crate-type = ["lib", "rlib"]
+
+[dependencies]
+soroban-sdk = { workspace = true }
+
+[dev-dependencies]
+soroban-sdk = { workspace = true, features = ["testutils"] }

stellar-lend/contracts/auction-types/src/lib.rs

@@ -0,0 +1,109 @@
+#![no_std]
+
+use soroban_sdk::{contracterror, contracttype, Address, BytesN};
+
+#[contracttype]
+#[derive(Clone, Debug, PartialEq)]
+pub enum AuctionState {
+    Pending,
+    Active,
+    PartiallyFilled,
+    FullyFilled,
+    Settled,
+    Cancelled,
+}
+
+#[contracttype]
+#[derive(Clone, Debug, PartialEq)]
+pub struct AuctionConfig {
+    pub starting_premium_bps: i128,
+    pub floor_discount_bps: i128,
+    pub auction_duration: u64,
+    pub price_decay_function: PriceDecayFunction,
+    pub min_bid_size: i128,
+    pub commit_phase_duration: u64,
+    pub reveal_phase_duration: u64,
+}
+
+#[contracttype]
+#[derive(Clone, Debug, PartialEq)]
+pub enum PriceDecayFunction {
+    Linear,
+    Exponential,
+}
+
+#[contracttype]
+#[derive(Clone, Debug, PartialEq)]
+pub struct Auction {
+    pub id: u64,
+    pub pool: Address,
+    pub user: Address,
+    pub collateral_asset: Address,
+    pub debt_asset: Address,
+    pub collateral_amount: i128,
+    pub debt_amount: i128,
+    pub start_time: u64,
+    pub end_time: u64,
+    pub starting_price: i128,
+    pub floor_price: i128,
+    pub current_price: i128,
+    pub remaining_collateral: i128,
+    pub filled_amount: i128,
+    pub state: AuctionState,
+    pub config: AuctionConfig,
+    pub created_at: u64,
+}
+
+#[contracttype]
+#[derive(Clone, Debug, PartialEq)]
+pub struct BidCommitment {
+    pub bidder: Address,
+    pub commitment_hash: BytesN<32>,
+    pub auction_id: u64,
+    pub timestamp: u64,
+}
+
+#[contracttype]
+#[derive(Clone, Debug, PartialEq)]
+pub struct BidReveal {
+    pub bidder: Address,
+    pub auction_id: u64,
+    pub collateral_amount: i128,
+    pub max_price: i128,
+    pub nonce: BytesN<32>,
+    pub timestamp: u64,
+}
+
+#[contracttype]
+#[derive(Clone, Debug, PartialEq)]
+pub struct BidResult {
+    pub auction_id: u64,
+    pub bidder: Address,
+    pub collateral_filled: i128,
+    pub price_paid: i128,
+    pub debt_repaid: i128,
+}
+
+#[contracterror]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
+#[repr(u32)]
+pub enum AuctionError {
+    AlreadyInitialized = 1,
+    NotAuthorized = 2,
+    AuctionNotFound = 3,
+    InvalidState = 4,
+    AuctionExpired = 5,
+    AuctionNotExpired = 6,
+    InsufficientCollateral = 7,
+    InvalidBidAmount = 8,
+    CommitmentAlreadyExists = 9,
+    CommitmentNotFound = 10,
+    RevealPhaseNotActive = 11,
+    InvalidReveal = 12,
+    BidTooLow = 13,
+    AlreadyFilled = 14,
+    InvalidConfig = 15,
+    AuctionStillActive = 16,
+    PositionHealthRestored = 17,
+    NoBidsReceived = 18,
+}

stellar-lend/contracts/liquidation-auction/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "liquidation-auction"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+crate-type = ["cdylib", "rlib"]
+
+[dependencies]
+soroban-sdk = { workspace = true }
+lending-types = { path = "../lending-types" }
+auction-types = { path = "../auction-types" }
+
+[dev-dependencies]
+soroban-sdk = { workspace = true, features = ["testutils"] }
+
+[[example]]
+name = "deploy"
+path = "examples/deploy.rs"
+crate-type = ["bin"]

stellar-lend/contracts/liquidation-auction/examples/deploy.rs

@@ -0,0 +1,11 @@
+use liquidation_auction::{LiquidationAuctionContract, LiquidationAuctionContractClient};
+use soroban_sdk::{Address, Env};
+
+// Example: deploy the contract
+pub fn deploy(env: &Env) {
+    let contract_id = env
+        .deployer()
+        .with_current_contract("")
+        .deploy(LiquidationAuctionContract);
+    let _client = LiquidationAuctionContractClient::new(env, &contract_id);
+}