Persist permanent indexing failures in the RAG index

app/MindWork AI Studio/Tools/Databases/IndexStore/IndexingFailureEntity.cs

@@ -0,0 +1,27 @@
+namespace AIStudio.Tools.Databases.IndexStore;
+
+internal sealed class IndexingFailureEntity
+{
+    public string ParentFileId { get; set; } = string.Empty;
+
+    public string DataSourceId { get; set; } = string.Empty;
+
+    public string AbsolutePath { get; set; } = string.Empty;
+
+    public string Fingerprint { get; set; } = string.Empty;
+
+    /// <summary>
+    /// The failure code, stored by name.
+    /// </summary>
+    /// <remarks>
+    /// The enum has no explicit numbers, so storing the name keeps the rows readable across
+    /// versions which add or reorder codes.
+    /// </remarks>
+    public string FailureCode { get; set; } = string.Empty;
+
+    public string FailureMessage { get; set; } = string.Empty;
+
+    public DateTimeOffset OccurredAtUtc { get; set; }
+
+    public EmbeddingStateDataSourceEntity? DataSource { get; set; }
+}