Add Stellar Soroban RPC source for on-chain AMM price discovery

[prodbycorne]

Overview

The current price sources (Stellar DEX orderbook, CoinGecko, CoinMarketCap) miss prices from Stellar's on-chain AMM liquidity pools. AMM pools often have tighter spreads and are the reference price for assets primarily traded on-chain. A Soroban/Horizon AMM source should be added as a fourth price source.

How Stellar AMMs Work

Stellar supports constant-product AMM pools (similar to Uniswap v2). The current price can be derived from:

price_A_in_B = reserve_B / reserve_A

Horizon exposes pool data at:
GET /liquidity_pools?reserves=XLM,USDC:ISSUER

Implementation

Create src/services/sources/stellarAmm.js:

const { Horizon } = require('@stellar/stellar-sdk');

async function fetchFromAMM(assetCode, issuer, horizonUrl) {
  const server = new Horizon.Server(horizonUrl);
  const pools = await server
    .liquidityPools()
    .forAssets(makeAsset(assetCode, issuer), makeAsset('XLM'))
    .call();

  if (!pools.records.length) return null;

  // Find deepest pool (highest total value)
  const best = pools.records.sort((a, b) =>
    parseFloat(b.total_shares) - parseFloat(a.total_shares)
  )[0];

  const [reserveA, reserveB] = best.reserves;
  const price = parseFloat(reserveB.amount) / parseFloat(reserveA.amount);
  return { price_usd: price * XLM_USD_PRICE, source: 'stellar_amm' };
}

Note: XLM_USD_PRICE is fetched from the existing Stellar DEX source.

Acceptance Criteria

• stellarAmm.js source created and registered in priceOracle.js
• Selects deepest pool by total shares
• Returns null if no AMM pool exists for the pair
• XLM-denominated prices converted to USD using current XLM price
• Added to fetchFromAllSources array
• Unit tests with mocked Horizon liquidity pool response
• AMM source included in circuit breaker system

[Fury03]

Hi Maintainer I can work on this issue and deliver fast

[matieuu1]

on-chain AMM pools often have tighter spreads and are the reference price for assets primarily traded on Stellar, but they're currently missing from our price oracle. I'll fetch pool data from Horizon, select the deepest pool by total shares, and integrate it into the circuit-breaker system with XLM-to-USD conversion.

[grantfox-oss]

🦊 GrantFox — @Fury03 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #36)
2. Your PR will be reviewed by the SmartDropLabs maintainers

Good luck! Track your progress on GrantFox.