previewOpenTrade

const preview = await client.previewOpenTrade({
  pairId: 0,
  isLong: true,
  collateral: 100,
  leverage: 10,
});

console.log(preview.entryPx);          // price after dynamic spread
console.log(preview.fees.total);       // deducted from collateral at open
console.log(preview.liquidationPx);

if (!preview.isValid) {
  console.warn(preview.warnings.map(w => w.code));
}

interface PreviewOpenTradeResult {
  pairId: string;
  pairFrom: string;
  pairTo: string;
  isLong: boolean;
  midPx: string;                 // live mid price
  refPx: string;                 // the side's bid/ask, or the limit price
  entryPx: string;               // expected execution price, after spread
  priceImpactP: string;          // dynamic spread applied, as a percentage
  spreadDecaySeconds: number;    // until the current imbalance spread decays to zero
  fees: {
    openFee: string;             // protocol opening fee
    oracleFee: string;           // flat price-retrieval fee
    builderFee: string;          // charged on notional; "0" with no builder
    builderFeeBps: string;
    total: string;               // deducted from collateral at open
    openFeePercent: string;      // blended rate actually applied
    takerFeePercent: string;
    makerFeePercent: string;
    takerNotional: string;
    makerNotional: string;
  };
  collateral: string;            // gross, as supplied
  collateralAtOpen: string;      // what actually backs the position, after fees
  exposure: string;              // collateralAtOpen × leverage
  positionSize: string;          // in base-asset units
  leverage: string;
  liquidationPx: string;
  effectiveMaxLeverage: string;  // accounts for the day-trade cap
  minLeverage: string;
  minPositionSize: string;
  isDayTrade: boolean;
  withinExposureLimit?: boolean; // undefined when the vault balance could not be read
  isValid: boolean;              // true when warnings is empty
  warnings: Array<{ code: string; message: string }>;
}