Fix FinTS transaction deduplication

convex/bank/fintsMap.ts

@@ -14,6 +14,54 @@ export type FintsStatementTransaction = {
   customerReference?: string;
 };
 
+const FINTS_EXTERNAL_REF_PLACEHOLDERS = new Set([
+  "0",
+  "00",
+  "000",
+  "0000",
+  "00000",
+  "000000",
+  "0000000",
+  "00000000",
+  "000000000",
+  "0000000000",
+  "KEINE",
+  "N/A",
+  "NA",
+  "NONE",
+  "NONREF",
+  "NOREF",
+  "NOTPROVIDED",
+  "NULL",
+  "UNBEKANNT",
+]);
+
+function normalizeFinTsExternalRefValue(value?: string): string | undefined {
+  const trimmed = value?.trim();
+  if (!trimmed) return undefined;
+
+  const compact = trimmed.replace(/[\s_-]+/g, "").toUpperCase();
+  if (
+    !compact ||
+    FINTS_EXTERNAL_REF_PLACEHOLDERS.has(compact) ||
+    /^POS\d+$/.test(compact)
+  ) {
+    return undefined;
+  }
+
+  return trimmed;
+}
+
+export function normalizeFinTsExternalRef(
+  bankReference?: string,
+  customerReference?: string,
+): string | undefined {
+  return (
+    normalizeFinTsExternalRefValue(bankReference) ??
+    normalizeFinTsExternalRefValue(customerReference)
+  );
+}
+
 export function formatFinTsDate(date: Date): string {
   const y = date.getFullYear();
   const m = String(date.getMonth() + 1).padStart(2, "0");
@@ -55,7 +103,7 @@ export function mapFinTsTransaction(
     vorgang,
     isPending: false,
     rawText: rawText || undefined,
-    externalRef: tx.bankReference || tx.customerReference || undefined,
+    externalRef: normalizeFinTsExternalRef(tx.bankReference, tx.customerReference),
     categoryName,
     assignedMonth,
     effectiveMonth,