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server/index.js

@@ -46,6 +46,7 @@ const {
 const {
   chargeKey,
   consumeCreditsWithIdempotency,
+  refundCreditsWithIdempotency,
   endpointKey,
   ensureBillingSchema,
   getAccountSnapshot,
@@ -757,9 +758,11 @@ app.post('/v1/billing/sync-revenuecat', async (request, response) => {
 
 app.post('/v1/scan', async (request, response) => {
   let userId = 'unknown';
+  let idempotencyKey = null;
+  let creditsCharged = 0;
   try {
     userId = ensureRequestAuth(request);
-    const idempotencyKey = ensureNonEmptyString(resolveIdempotencyKey(request), 'Idempotency-Key header');
+    idempotencyKey = ensureNonEmptyString(resolveIdempotencyKey(request), 'Idempotency-Key header');
     const imageUri = ensureNonEmptyString(request.body?.imageUri, 'imageUri');
     const language = normalizeLanguage(request.body?.language);
     const endpointId = endpointKey('scan', userId, idempotencyKey);
@@ -770,7 +773,6 @@ app.post('/v1/scan', async (request, response) => {
       return;
     }
 
-    let creditsCharged = 0;
     const modelPath = [];
     let modelUsed = null;
     let modelFallbackCount = 0;
@@ -936,6 +938,19 @@ app.post('/v1/scan', async (request, response) => {
     response.status(200).json(payload);
   } catch (error) {
     console.error(`Scan error for user ${userId}:`, error);
+    if (error?.code === 'NOT_A_PLANT' && creditsCharged > 0 && idempotencyKey) {
+      try {
+        const refunded = await refundCreditsWithIdempotency(
+          db,
+          userId,
+          chargeKey('scan-refund', userId, idempotencyKey),
+          creditsCharged,
+        );
+        console.log(`Refunded ${refunded} credit(s) for user ${userId} (NOT_A_PLANT)`);
+      } catch (refundError) {
+        console.error(`Failed to refund credits for user ${userId} (NOT_A_PLANT):`, refundError);
+      }
+    }
     const payload = toApiErrorPayload(error);
     response.status(payload.status).json(payload.body);
   }

server/lib/billing.js

@@ -623,6 +623,37 @@ const consumeCreditsWithIdempotency = async (db, userId, key, cost) => {
   });
 };
 
+const refundCredits = (account, amount) => {
+  if (amount <= 0) return 0;
+
+  // Spiegelbildlich zu consumeCredits: zuerst das Monatskontingent entlasten,
+  // ein etwaiger Rest wandert auf das Topup-Guthaben zurück.
+  let remaining = amount;
+  const monthlyRefund = Math.min(account.usedThisCycle, remaining);
+  account.usedThisCycle -= monthlyRefund;
+  remaining -= monthlyRefund;
+
+  if (remaining > 0) {
+    account.topupBalance += remaining;
+  }
+
+  return amount;
+};
+
+const refundCreditsWithIdempotency = async (db, userId, key, amount) => {
+  return runInTransaction(db, async (tx) => {
+    const existing = await readIdempotentValue(tx, key);
+    if (existing && typeof existing.refunded === 'number') return existing.refunded;
+
+    const account = await getOrCreateAccount(tx, userId);
+    const refunded = refundCredits(account, amount);
+    account.updatedAt = nowIso();
+    await upsertAccount(tx, account);
+    await writeIdempotentValue(tx, key, { refunded });
+    return refunded;
+  });
+};
+
 const getBillingSummary = async (db, userId) => {
   if (userId === 'guest') {
     return {
@@ -820,6 +851,7 @@ module.exports = {
   chargeKey,
   claimNotificationOnce,
   consumeCreditsWithIdempotency,
+  refundCreditsWithIdempotency,
   endpointKey,
   ensureBillingSchema,
   getAccountSnapshot,