Stopped indexing runs whose embedding settings changed (#1051)

app/MindWork AI Studio/Tools/Services/DataSourceRunSignature.cs

@@ -0,0 +1,18 @@
+namespace AIStudio.Tools.Services;
+
+/// <summary>
+/// The embedding settings an indexing run of a data source works for.
+/// </summary>
+/// <remarks>
+/// Deliberately nothing but the embedding signature, which decides when a stored index is thrown
+/// away. A run counts as outdated exactly when the next run would throw its work away, and a list of
+/// fields of its own would have to be kept in step with that signature by hand.
+/// </remarks>
+/// <param name="EmbeddingSignature">The embedding signature of the run, cf. DataSourceEmbeddingService.BuildEmbeddingSignature.</param>
+internal sealed record DataSourceRunSignature(string EmbeddingSignature)
+{
+    /// <summary>
+    /// No run would start: the data source or its embedding provider is gone, or that provider may not read it.
+    /// </summary>
+    public static readonly DataSourceRunSignature NONE = new(string.Empty);
+}