feat(sep-38): aggregate RFQ quotes with Stellar DEX order book depth …

[Killerjunior]

feat(sep-38): aggregate RFQ quotes with Stellar DEX order book depth (#347)

Summary

Aggregates SEP-38 RFQ quotes across Stellar DEX order book depth via Horizon, calculating volume-weighted average execution prices, slippage, and price impact with a 2-second cache TTL. It also updates the frontend TradeForm to display order book depth, estimated slippage, and a "Best Price" badge for optimal fills.

Type of change

• Bug fix
• New feature
• Documentation update
• Refactor / chore
• Smart contract change

Related issue

Closes #347

Changes

• Backend Order Book Service (backend/src/services/sep/orderBookService.js):
  • Implemented parseAsset supporting SEP-38 identifiers (stellar:native, stellar:CODE:ISSUER, shorthand assets).
  • Implemented getOrderBook with Horizon /order_book integration and a 2-second Redis/LRU cache TTL.
  • Implemented calculateWeightedPrice to walk order book depth levels, compute volume-weighted execution prices, and handle partial fills.
  • Implemented estimateSlippage to calculate execution slippage against top-of-book and price impact against the marginal fill level.
• Backend SEP-38 Service & API Routes (backend/src/services/sep/sep38Service.js, backend/src/routes/sep38.js, backend/src/server.js):
  • Added getAggregatedQuote method returning execution price, top-of-book price, slippage %, price impact %, levels consumed, and partial fill indicators.
  • Added GET /api/v1/sep38/quote/aggregated and GET /sep38/quote/aggregated endpoints with full query validation (sell_asset, buy_asset, sell_amount).
  • Mounted /api/v1/sep38 routes in server.js.
• Frontend Swap Interface (frontend/components/TradeForm.tsx):
  • Integrated fetchAggregatedQuote with client-side 2-second caching.
  • Added "Best Price" badge indicator in the swap preview when aggregated depth provides optimal fill pricing.
  • Displayed order book depth (levels consumed) and estimated slippage in the swap preview panel.
• Unit & Integration Tests:
  • Added backend/__tests__/orderBook.test.js and updated backend/__tests__/sep38.test.js (single-level fill, multi-level depth fill, partial fill, 2s cache TTL).
  • Added frontend test suite in frontend/__tests__/TradeForm.test.tsx for aggregated quotes, Best Price badge, and depth display.

Testing

• Tested locally on Testnet
• Added/updated unit tests
• Manually tested UI flow

Test Results:

• backend: jest __tests__/orderBook.test.js __tests__/sep38.test.js (25/25 tests passing)
• frontend: jest __tests__/TradeForm.test.tsx (41/41 tests passing)
• Linting & Formatting: ESLint passed with 0 errors; Prettier formatting verified.

Screenshots (if UI change)

Aggregated quote details and "Best Price" badge rendered in the TradeForm swap preview.

Checklist

• My code follows the project style
• I've updated docs if needed
• No console errors or warnings
• I've rebased on latest main

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