fix: make NpgsqlDataSource optional in EmbeddingService to allow test isolation

NpgsqlDataSource is an abstract class with no default constructor, so
Moq/Castle.DynamicProxy cannot create a proxy for it. Since the upload
path (staging-swap) is the only code that needs the data source, and
AISearchServiceTests only exercise the search path, making the parameter
optional (nullable) with a lazy null check fixes test isolation without
weakening production safety.

Author: BenjaminMichaelis

EssentialCSharp.Chat.Shared/Services/EmbeddingService.cs

@@ -13,7 +13,7 @@ namespace EssentialCSharp.Chat.Common.Services;
 public class EmbeddingService(
     VectorStore vectorStore,
     IEmbeddingGenerator<string, Embedding<float>> embeddingGenerator,
-    NpgsqlDataSource dataSource)
+    NpgsqlDataSource? dataSource = null)
 {
     public static string CollectionName { get; } = "markdown_chunks";
 
@@ -59,6 +59,10 @@ public async Task GenerateBookContentEmbeddingsAndUploadToVectorStore(
     {
         collectionName ??= CollectionName;
 
+        if (dataSource is null)
+            throw new InvalidOperationException(
+                $"{nameof(NpgsqlDataSource)} must be provided to upload embeddings. Ensure it is registered in DI.");
+
         if (!_safeIdentifierRegex.IsMatch(collectionName))
             throw new ArgumentException(
                 $"Collection name '{collectionName}' contains unsafe characters. Use only letters, digits, and underscores.",

EssentialCSharp.Chat.Tests/AISearchServiceTests.cs

@@ -33,8 +33,9 @@ private static (AISearchService svc, Mock<VectorStoreCollection<string, BookCont
                 It.IsAny<CancellationToken>()))
             .ReturnsAsync(new GeneratedEmbeddings<Embedding<float>>([new Embedding<float>(new float[1536])]));
 
-        var dataSourceMock = new Mock<NpgsqlDataSource>();
-        var embeddingService = new EmbeddingService(vectorStoreMock.Object, embGenMock.Object, dataSourceMock.Object);
+        // NpgsqlDataSource has no default constructor so Moq cannot proxy it.
+        // The upload path is not exercised by these tests, so pass null.
+        var embeddingService = new EmbeddingService(vectorStoreMock.Object, embGenMock.Object);
         var loggerMock = new Mock<ILogger<AISearchService>>();
 
         return (new AISearchService(vectorStoreMock.Object, embeddingService, loggerMock.Object), collectionMock);