Testfundament aufbauen und Bestandsaufnahme dokumentieren

IChatCompletionClient aus OpenRouterClient extrahiert, damit AgentEngine und
ContextCompactor ohne echte API-Aufrufe testbar sind.

Neues Testprojekt tests/ClawdDotNet.Core.Tests (xUnit, Shouldly, NSubstitute,
FsCheck) mit:
- FakeChatClient (programmierbare Antwortfolgen, Deep-Copy der Requests)
- ContextInvariants (prueft die API-Regeln fuer tool_call-Paarung)
- Conversation-Builder fuer gueltige Testkonversationen
- 26 Tests: Compaction, LoopGuard, 2 Property-Tests

10 Tests sind bewusst rot — sie reproduzieren die Bugs B1, B3 und B14 aus der
Bestandsaufnahme und werden mit den Fixes gruen.

Ausserdem: fehlende Tool-Projekte in slnx ergaenzt, Test-Pakete im
packageSourceMapping der NuGet.Config eingetragen.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ClawdDotNet.Core/Api/IChatCompletionClient.cs

@@ -0,0 +1,12 @@
+using ClawdDotNet.Core.Api.Models;
+
+namespace ClawdDotNet.Core.Api;
+
+/// <summary>
+/// Abstraktion über den Chat-Completion-Endpunkt.
+/// Erlaubt es, Engine und Compactor ohne echte API-Aufrufe zu testen.
+/// </summary>
+public interface IChatCompletionClient
+{
+    Task<ChatResponse> CompleteAsync(ChatRequest request, CancellationToken ct);
+}

src/ClawdDotNet.Core/Api/OpenRouterClient.cs

@@ -6,7 +6,7 @@ using Microsoft.Extensions.Logging;
 
 namespace ClawdDotNet.Core.Api;
 
-public sealed class OpenRouterClient : IDisposable
+public sealed class OpenRouterClient : IChatCompletionClient, IDisposable
 {
     private const string BaseUrl = "https://openrouter.ai/api/v1/";
 

src/ClawdDotNet.Core/Engine/AgentEngine.cs

@@ -12,7 +12,7 @@ namespace ClawdDotNet.Core.Engine;
 
 public sealed class AgentEngine : IAgentMessageRouter
 {
-    private readonly OpenRouterClient _client;
+    private readonly IChatCompletionClient _client;
     private readonly ToolRegistry _toolRegistry;
     private readonly PermissionGate _permissionGate;
     private readonly IStateStore _stateStore;
@@ -35,7 +35,7 @@ public sealed class AgentEngine : IAgentMessageRouter
     };
 
     public AgentEngine(
-        OpenRouterClient client,
+        IChatCompletionClient client,
         ToolRegistry toolRegistry,
         PermissionGate permissionGate,
         IStateStore stateStore,

src/ClawdDotNet.Core/Engine/ContextCompactor.cs

@@ -7,14 +7,14 @@ namespace ClawdDotNet.Core.Engine;
 
 public sealed class ContextCompactor
 {
-    private readonly OpenRouterClient _client;
+    private readonly IChatCompletionClient _client;
     private readonly ILogger _logger;
 
     private const int ProtectedTailMessages = 6;
     private const int MaxToolResultChars = 2000;
     private const string TruncatedMarker = "\n\n[... Ergebnis gekürzt ...]";
 
-    public ContextCompactor(OpenRouterClient client, ILoggerFactory loggerFactory)
+    public ContextCompactor(IChatCompletionClient client, ILoggerFactory loggerFactory)
     {
         _client = client;
         _logger = loggerFactory.CreateLogger("ClawdDotNet.Core.Engine.ContextCompactor");