fix: validate duplicate operation UUIDs

backend/src/services/import.ts

@@ -133,12 +133,20 @@ function validateSemantics(data: StatementFile): ValidationError | null {
   }
 
   const fps = new Set<string>();
+  const operationIds = new Set<string>();
   for (let i = 0; i < data.transactions.length; i++) {
     const fp = computeFingerprint(data.statement.accountNumber, data.transactions[i]);
     if (fps.has(fp)) {
       return { status: 422, error: 'VALIDATION_ERROR', message: `Duplicate fingerprint found within file at transaction index ${i}` };
     }
     fps.add(fp);
+    const operationId = data.transactions[i].operationId;
+    if (operationId) {
+      if (operationIds.has(operationId.toLowerCase())) {
+        return { status: 422, error: 'VALIDATION_ERROR', message: `Duplicate operationId found within file at transaction index ${i}` };
+      }
+      operationIds.add(operationId.toLowerCase());
+    }
   }
 
   return null;