Step 5: Update exchange price endpoint to use new pricing config

- Update ExchangeConfigResponse schema with direction-specific fields
- Remove premium_percentage from PriceResponse (now in config)
- Update price endpoint to load pricing config from database
- Update frontend to use direction-specific min/max and calculate premium
- Update tests to seed pricing config
- Add logic to clamp amount when direction changes

frontend/app/exchange/components/PriceDisplay.tsx

@@ -13,6 +13,7 @@ interface PriceDisplayProps {
   lastUpdate: Date | null;
   direction: "buy" | "sell";
   agreedPrice: number;
+  premiumPercent: number;
 }
 
 /**
@@ -94,10 +95,10 @@ export function PriceDisplay({
   lastUpdate,
   direction,
   agreedPrice,
+  premiumPercent,
 }: PriceDisplayProps) {
   const t = useTranslation("exchange");
   const marketPrice = priceData?.price?.market_price ?? 0;
-  const premiumPercent = priceData?.price?.premium_percentage ?? 5;
   const isPriceStale = priceData?.price?.is_stale ?? false;
 
   return (

frontend/app/exchange/page.tsx

@@ -116,24 +116,42 @@ export default function ExchangePage() {
 
   // Config from API
   const config = priceData?.config;
-  const eurMin = config?.eur_min ?? 100;
-  const eurMax = config?.eur_max ?? 3000;
+  const eurMinBuy = config?.eur_min_buy ?? 10000;
+  const eurMaxBuy = config?.eur_max_buy ?? 300000;
+  const eurMinSell = config?.eur_min_sell ?? 10000;
+  const eurMaxSell = config?.eur_max_sell ?? 300000;
   const eurIncrement = config?.eur_increment ?? 20;
 
+  // Get direction-specific min/max
+  const eurMin = direction === "buy" ? eurMinBuy : eurMinSell;
+  const eurMax = direction === "buy" ? eurMaxBuy : eurMaxSell;
+
   // Compute trade details
   const price = priceData?.price;
   const marketPrice = price?.market_price ?? 0;
-  const premiumPercent = price?.premium_percentage ?? 5;
+  const premiumBuy = config?.premium_buy ?? 5;
+  const premiumSell = config?.premium_sell ?? 5;
+  const smallTradeThreshold = config?.small_trade_threshold_eur ?? 0;
+  const smallTradeExtraPremium = config?.small_trade_extra_premium ?? 0;
 
-  // Calculate agreed price based on direction
+  // Calculate total premium: base premium for direction + extra if small trade
+  const totalPremiumPercent = useMemo(() => {
+    const basePremium = direction === "buy" ? premiumBuy : premiumSell;
+    if (eurAmount <= smallTradeThreshold) {
+      return basePremium + smallTradeExtraPremium;
+    }
+    return basePremium;
+  }, [direction, premiumBuy, premiumSell, eurAmount, smallTradeThreshold, smallTradeExtraPremium]);
+
+  // Calculate agreed price based on direction and total premium
   const agreedPrice = useMemo(() => {
     if (!marketPrice) return 0;
     if (direction === "buy") {
-      return marketPrice * (1 + premiumPercent / 100);
+      return marketPrice * (1 + totalPremiumPercent / 100);
     } else {
-      return marketPrice * (1 - premiumPercent / 100);
+      return marketPrice * (1 - totalPremiumPercent / 100);
     }
-  }, [marketPrice, premiumPercent, direction]);
+  }, [marketPrice, totalPremiumPercent, direction]);
 
   // Calculate sats amount
   const satsAmount = useMemo(() => {
@@ -155,6 +173,15 @@ export default function ExchangePage() {
     }
   }, [isLightningDisabled, bitcoinTransferMethod]);
 
+  // Clamp amount when direction changes (min/max may differ per direction)
+  useEffect(() => {
+    if (eurAmount < eurMin) {
+      setEurAmount(eurMin);
+    } else if (eurAmount > eurMax) {
+      setEurAmount(eurMax);
+    }
+  }, [direction, eurMin, eurMax]); // eslint-disable-line react-hooks/exhaustive-deps
+
   // Fetch slots when date is selected
   useEffect(() => {
     if (selectedDate && user && isAuthorized) {
@@ -307,6 +334,7 @@ export default function ExchangePage() {
           lastUpdate={lastPriceUpdate}
           direction={direction}
           agreedPrice={agreedPrice}
+          premiumPercent={totalPremiumPercent}
         />
 
         {/* Step Indicator */}
@@ -322,8 +350,8 @@ export default function ExchangePage() {
             eurAmount={eurAmount}
             onEurAmountChange={setEurAmount}
             satsAmount={satsAmount}
-            eurMin={eurMin}
-            eurMax={eurMax}
+            eurMin={eurMin / 100}
+            eurMax={eurMax / 100}
             eurIncrement={eurIncrement}
             isPriceStale={isPriceStale}
             hasPrice={!!priceData?.price}