Fix Jasmin customer key and amount mapping

tests/test_external_reconciliation_jasmin_mapping.py

@@ -0,0 +1,38 @@
+from app.external_reconciliation_sync import _external_customer_key, _jasmin_amount
+
+
+def test_jasmin_customer_key_prefers_party_code_over_document_natural_key():
+    record = {
+        "naturalKey": "ORC.ORC2026.136",
+        "buyerCustomerParty": "0569",
+        "accountingParty": "0569",
+    }
+
+    assert _external_customer_key(record, source_system="jasmin") == "0569"
+
+
+def test_jasmin_customer_key_does_not_use_document_natural_key():
+    record = {"naturalKey": "ORC.ORC2026.136", "id": "document-uuid"}
+
+    assert _external_customer_key(record, source_system="jasmin") == ""
+
+
+def test_jasmin_amount_reads_flattened_payable_total():
+    record = {
+        "payableAmountAmount": 441.57,
+        "grossValueAmount": 359.00,
+    }
+
+    assert _jasmin_amount(record) == "441.57"
+
+
+def test_jasmin_amount_reads_nested_money_object():
+    record = {
+        "payableAmount": {
+            "amount": 441.57,
+            "baseAmount": 441.57,
+            "reportingAmount": 441.57,
+        }
+    }
+
+    assert _jasmin_amount(record) == "441.57"