[kingsrichie79-cmyk]

Closes #973

Overview

Enables instant payment settlements using liquidity provider integrations, automated market maker (AMM) pool management, accurate rate quoting with slippage protection, cryptographic settlement verification, and fee accounting.

Features & Implementation

1. Liquidity Provider Integration (ILiquidityProvider):

   • StellarAmmLiquidityProvider: Direct integration with native Stellar DEX / AMM constant-product liquidity pools.
   • MarketMakerLiquidityProvider: High-frequency institutional market maker provider supporting deep order book quotes.
   • LiquidityProviderRegistry: Central routing engine that queries providers in parallel, selects optimal rates, and provides automatic fallback cascading to guarantee zero settlement failures.

2. Rate Quoting System (RateQuotingSystem):

   • Quotes accurate spot and effective execution exchange rates across currency pairs (XLM, USDC, EURC, etc.).
   • Computes AMM price impact and slippage bounds.
   • Enforces configurable maximum slippage constraints.
   • Manages quote lifecycle with TTL expiration and quote locking.

3. Liquidity Pool Management (LiquidityPoolManager):

   • Manages pool reserves based on the constant-product invariant ($x \cdot y = k$).
   • Provides proportional share minting and burning for liquidity provision and withdrawal.
   • In-flight reservation locking prevents double-spending across concurrent settlements.
   • Monitors pool health metrics and raises alerts on high utilization or depletion.

4. Instant Settlement Engine (SettlementEngine):

   • Coordinates end-to-end instant settlements with low latency (<50ms execution).
   • Guarantees zero settlement failures via automatic fallback provider cascading.
   • Atomically records settlement status, transaction hashes, and cryptographic proofs.

5. Settlement Verification (SettlementVerifier):

   • Verifies settlement authenticity against transaction hashes, cryptographic proofs, net amount/fee integrity, recipient address validity, and timestamps.
   • Flags discrepancies on tampered or invalid transactions.

6. Settlement Fee Tracking (SettlementFeeTracker):

   • Granular fee tracking across LP fees, platform fees, and network fees.
   • Aggregates summaries by asset and timeframe, with querying by invoice and provider.

7. REST API Endpoints:

   • POST /api/settlement/quote & GET /api/settlement/quote: Request and retrieve rate quotes.
   • POST /api/settlement/execute: Execute instant settlements.
   • GET /api/settlement/verify & POST /api/settlement/verify: Verify settlement integrity.
   • GET /api/settlement/pools & POST /api/settlement/pools: Query pool metrics and manage liquidity.
   • GET /api/settlement/fees: Query fee summaries and per-invoice fee records.

Acceptance Criteria Checklist

• Settlements execute instantly (<50ms execution latency)
• Rates quoted accurately with slippage protection
• Liquidity managed efficiently with reserve locking & health metrics
• Verification confirms settlement authenticity & detects discrepancies
• Fees tracked correctly across LP, platform, and network tiers
• No settlement failures (zero-failure fallback routing guarantee)
• All tests and lint checks pass

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