Codebasis als Dateien ins Arbeitsrepo statt als Gitlink

QuellCode/CentronERP war nur als Gitlink (Submodul-Referenz auf 79c1142)
getrackt, ohne .gitmodules und ohne erreichbares Remote. Der
Untersuchungsgegenstand der Versuchsreihe war damit nicht reproduzierbar
gesichert: Ein Klon haette ein leeres Verzeichnis erhalten, und die Belege
der 3.287 Anforderungen waeren nicht ueberpruefbar gewesen.

Umstellung:
- Historie nach c:\DEV\CentronERP_git_snapshot_79c1142 ausgelagert
  (vollstaendig lesbar, enthaelt 79c1142 und Vorgaenger 89ccfd6)
- Gitlink aus dem Index entfernt
- Dateiinhalt aufgenommen: 24.557 Dateien, rund 333 MB

Die verschachtelte .gitignore der Codebasis gilt weiter, Build-Artefakte
bleiben ausgeschlossen. Details in Versuche/Versuch_01/_Codebasis-Nachweis.md

QuellCode/CentronERP/tests/backend/Centron.Tests.BL/DataExchange/BookKeeping/Abacus/BookKeepingExportAbacusTest.cs

@@ -0,0 +1,112 @@
+using System;
+using System.Collections.Generic;
+using System.Xml.Linq;
+using Centron.Data.Entities.DataExchange.BookKeeping.Export;
+using Centron.Gateway.DataExchange.BookKeeping.Abacus;
+using Centron.Interfaces.DataExchange.BookKeeping;
+using NSubstitute;
+
+namespace Centron.Tests.BL.DataExchange.BookKeeping.Abacus;
+
+public class BookKeepingExportAbacusTest
+{
+    [Theory]
+    [InlineData("2024.00")]
+    [InlineData("2023.00")]
+    [InlineData("2020.00")]
+    public void SupplierReceiptExport_DoesNotWriteTaxTransferTypeForModernKreditorVersions(string kreditorReceiptVersion)
+    {
+        var result = CreateExport(kreditorReceiptVersion);
+
+        var document = XDocument.Parse((string)result.File);
+        Assert.Empty(document.Descendants("TaxTransferType"));
+        Assert.Equal("KRED", document.Root?.Element("Task")?.Element("Parameter")?.Element("Application")?.Value);
+        Assert.Equal("Document", document.Root?.Element("Task")?.Element("Parameter")?.Element("Id")?.Value);
+        Assert.Equal(kreditorReceiptVersion, document.Root?.Element("Task")?.Element("Parameter")?.Element("Version")?.Value);
+    }
+
+    [Theory]
+    [InlineData("2018.00")]
+    [InlineData("2015.00")]
+    public void SupplierReceiptExport_WritesTaxTransferTypeForLegacyKreditorVersions(string kreditorReceiptVersion)
+    {
+        var result = CreateExport(kreditorReceiptVersion);
+
+        var document = XDocument.Parse((string)result.File);
+        var taxTransferType = Assert.Single(document.Descendants("TaxTransferType"));
+        Assert.Equal("0", taxTransferType.Value);
+        Assert.Equal(kreditorReceiptVersion, document.Root?.Element("Task")?.Element("Parameter")?.Element("Version")?.Value);
+    }
+
+    private static IBookKeepingReceiptExportFileGeneratorResult CreateExport(string kreditorReceiptVersion)
+    {
+        var sut = new BookKeepingExportAbacus();
+        var result = sut.GetReceiptsBookingData(
+            new[] { CreateSupplierReceipt() },
+            CreateSettings(kreditorReceiptVersion),
+            CreateUserSettings(),
+            customInterfaceSettings: null,
+            customInterfaceColumns: null);
+
+        Assert.True(result.IsSuccessful, result.Message);
+        Assert.Empty(result.FailedList);
+
+        return result;
+    }
+
+    private static BookKeepingExportConfiguration CreateSettings(string kreditorReceiptVersion)
+    {
+        return new BookKeepingExportConfiguration
+        {
+            KreditorReceiptVersion = kreditorReceiptVersion,
+            ReceiptsExportAllPositions = true
+        };
+    }
+
+    private static BookKeepingExportUserSettings CreateUserSettings()
+    {
+        return new BookKeepingExportUserSettings
+        {
+            ExportDateFrom = new DateTime(2026, 1, 1),
+            ExportDateTo = new DateTime(2026, 1, 31)
+        };
+    }
+
+    private static IBookKeepingReceipt CreateSupplierReceipt()
+    {
+        var receipt = Substitute.For<IBookKeepingReceipt>();
+        receipt.Number.Returns(4711);
+        receipt.Date.Returns(new DateTime(2026, 1, 15));
+        receipt.ExternalReceiptDate.Returns(new DateTime(2026, 1, 14));
+        receipt.ExternalReceiptNumber.Returns("EXT-4711");
+        receipt.Type.Returns(BookKeepingReceiptKind.SupplierInvoice);
+        receipt.AddressBookKeepingNumber.Returns("70001");
+        receipt.CurrencyISOCode.Returns("CHF");
+        receipt.PaymentTypeNumber.Returns("30");
+        receipt.BankNumber.Returns(1);
+        receipt.NetPriceComplete.Returns(100m);
+        receipt.TaxPriceComplete.Returns(8.1m);
+        receipt.NetPriceFCComplete.Returns(100m);
+        receipt.TaxPriceFCComplete.Returns(8.1m);
+        var item = CreateReceiptItem();
+        receipt.Items.Returns(new List<IBookKeepingReceiptItem> { item });
+
+        return receipt;
+    }
+
+    private static IBookKeepingReceiptItem CreateReceiptItem()
+    {
+        var item = Substitute.For<IBookKeepingReceiptItem>();
+        item.Position.Returns(1);
+        item.ProfitAndLossAccount.Returns(4000);
+        item.NetPriceTotalComplete.Returns(100m);
+        item.TaxPriceTotalComplete.Returns(8.1m);
+        item.NetPriceTotalFCComplete.Returns(100m);
+        item.TaxPriceTotalFCComplete.Returns(8.1m);
+        item.TaxRate.Returns(8.1m);
+        item.VATCode.Returns("81");
+        item.Text.Returns("Test position");
+
+        return item;
+    }
+}