Fixed Semantic Search with external data sources (ERI servers) (#1090)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/MindWork AI Studio/Tools/RAG/UnreachableDataSources.cs

@@ -0,0 +1,32 @@
+using System.Text;
+
+using AIStudio.Settings;
+
+namespace AIStudio.Tools.RAG;
+
+/// <summary>
+/// Tells the model which data sources of the chat could not be searched because their server could not be reached.
+/// </summary>
+/// <remarks>
+/// Semantic Search writes this into the description of its tool, the classic RAG process next to
+/// the passages it found. Both use the same words, so that the model hears the same in either way.
+/// Only external data sources have a server which may be out of reach, hence their kind is not
+/// listed.<br/><br/>
+/// The note holds nothing but the names the data sources have in AI Studio, configured by the user
+/// or the organization, and no word of their servers. It therefore needs no prompt-injection filter,
+/// like the rest of the description of the tool.
+/// </remarks>
+public static class UnreachableDataSources
+{
+    /// <summary>
+    /// Writes the note on the given data sources.
+    /// </summary>
+    /// <param name="builder">The builder to write into.</param>
+    /// <param name="dataSources">The data sources whose server could not be reached, in the order to list them.</param>
+    public static void AppendTo(StringBuilder builder, IReadOnlyList<IDataSource> dataSources)
+    {
+        builder.AppendLine("These external data sources of this chat could not be reached or signed in to right now, so they cannot be searched. Their content is missing rather than empty; tell the user so when a question concerns them:");
+        foreach (var dataSource in dataSources)
+            builder.AppendLine($"- name='{dataSource.Name}'");
+    }
+}