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/docs/reference/receipts/Contract-Billing-RMM-Article-Logic.md

@@ -0,0 +1,123 @@
+# RMM-Article Logic in Contract Billing
+
+## Overview
+
+The Remote Monitoring Management (RMM) Article functionality in c-entron.NET allows for automatic billing of usage-based services that are measured by an external RMM system. This document outlines the rules, workflow, and technical implementation of the RMM Article billing process.
+
+## Key Concepts
+
+### RMM System Integration
+- The c-entron.NET application integrates with external RMM systems (e.g., "Riverbird") to retrieve usage statistics
+- Usage data is collected for specified periods and used to calculate billing amounts
+- Communication happens via the `RiverConnectionBL` class which connects to the RMM service
+
+### Contract Article References
+- Each billable RMM item is defined as a `ContractArticleReferenzes` entity
+- These references link articles in c-entron.NET to specific metrics in the RMM system
+- Article references contain configuration for billing calculation rules
+
+## Workflow
+
+### 1. Contract Configuration
+1. A contract is configured to use RMM billing (`WhetherRMM` returns true)
+2. Contract article references are configured, specifying:
+   - Article type (e.g., server, workstation)
+   - Article reference (linking to the inventory item)
+   - Pricing rules
+
+### 2. Invoice Generation Process
+1. During the `CreateInvoiceToContractComplete` process, `CheckRMMArticle` is called
+2. The system checks if the contract has RMM enabled
+3. The system looks for a placeholder tag `@@RMMArtikel@@` in the invoice template
+4. Contract article references are retrieved for the specific contract
+5. The system queries the external RMM service for usage data in the billing period
+6. For each article reference with available usage data:
+   - Usage amount is calculated using `CalculateContractBillingAmount`
+   - An invoice line item is created with the calculated amount
+   - Descriptive text is added explaining the service type
+   - The item is inserted at the position marked by `@@RMMArtikel@@` or near the end of the invoice
+
+### 3. Placeholder Handling
+- If the invoice template contains a text element with `@@RMMArtikel@@`, it serves as a position marker
+- This placeholder is removed and replaced with the actual RMM article items
+- If no placeholder is found, RMM items are inserted near the end of the invoice (count - 2 position)
+
+## Error Handling
+
+### External Service Unavailability
+- If the RMM service is unavailable during invoice generation, and the contract requires RMM data:
+  - An `RMMServiceUnavailableException` is thrown
+  - The invoice creation process is aborted
+  - An error message is logged with details about the failure
+- This prevents invoices from being created with incomplete usage data, ensuring customers are billed correctly
+
+### Data Integrity Rules
+- When a parent entity is deleted (State = 0), related child entities should also be marked as deleted
+- This ensures data consistency when RMM configurations change
+
+## Technical Implementation Details
+
+### RMM Article Detection
+```csharp
+var rmmItem = invoice.Items.FirstOrDefault(f => 
+    (f.RichText != null && f.RichText.IndexOf("@@RMMArtikel@@", StringComparison.InvariantCulture) > -1) ||
+    (f.Text != null && f.Text.IndexOf("@@RMMArtikel@@", StringComparison.InvariantCulture) > -1));
+```
+
+### Usage Data Retrieval
+```csharp
+var riverbirdStatisticsResult = new RiverConnectionBL(this.Session).GetContractBillingAmounts(
+    billingParam.InvoiceFrom.Value, 
+    billingParam.InvoiceTo.Value.AddDays(1), 
+    invoice.CustomerI3D, 
+    rmmArticleReferences);
+```
+
+### Error Handling for Service Unavailability
+```csharp
+if (riverbirdStatisticsResult.Status is ResultStatus.Error)
+{
+    // Only throw exception when RMM articles are expected
+    if (rmmItem != null || rmmArticleReferences.Any())
+    {
+        string errorMsg = $"Die Rechnung kann nicht erstellt werden, da der RMM-Service nicht erreichbar ist. " +
+                          $"Fehlermeldung: {riverbirdStatisticsResult.Message}";
+        _logger.Error(errorMsg);
+        throw new RMMServiceUnavailableException(errorMsg);
+    }
+    return;
+}
+```
+
+## Best Practices
+
+1. **Service Configuration**
+   - Ensure the RMM service URL is properly configured in application settings
+   - Verify authentication tickets are valid for the RMM service
+
+2. **Contract Setup**
+   - Associate correct article references with appropriate RMM metrics
+   - Set proper calculation rules for each article type
+
+3. **Invoice Templates**
+   - Include the `@@RMMArtikel@@` placeholder in invoice templates where RMM items should appear
+   - Ensure proper formatting and positioning for RMM article items
+
+4. **Monitoring**
+   - Monitor logs for RMM service connectivity issues
+   - Periodically verify that usage data is being correctly retrieved and calculated
+
+## Troubleshooting
+
+| Problem | Possible Cause | Solution |
+|---------|---------------|----------|
+| No RMM items in invoice | RMM not enabled for contract | Check contract configuration |
+| No RMM items in invoice | No usage data in RMM system | Verify usage data in RMM system |
+| Invoice creation fails | RMM service unavailable | Check network connectivity and service status |
+| Incorrect billing amounts | Calculation rules misconfigured | Review article reference configuration |
+
+## Related Components
+
+- `AutomaticFacturaWebServiceBL` - Main billing logic
+- `RiverConnectionBL` - Handles communication with RMM service
+- `ContractArticleReferenzes` - Defines article references for RMM billing