Added a way to read what the AI received from your sources (#1100)

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

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

@@ -0,0 +1,48 @@
+using System.Text;
+
+namespace AIStudio.Tools.RAG;
+
+/// <summary>
+/// A retrieval context as the AI receives it: filtered for prompt injections, written out, and
+/// ready to be numbered.
+/// </summary>
+/// <remarks>
+/// Made by IRetrievalContextExtensions.PrepareForModelAsync. Which number a context gets depends on
+/// which contexts the caller hands on in the end, so the header is written only then, see
+/// ToMarkdown. The app writes it itself, which is why it needs no filter.
+/// </remarks>
+/// <param name="Context">The context as the data source delivered it.</param>
+/// <param name="Body">What the AI is told about the context below its header: the filtered description, then the filtered content.</param>
+/// <param name="Sources">The sources the context lends to the answer, which may be none.</param>
+/// <param name="Passage">What the user is shown of the context, or null when the context has no source to list it under.</param>
+public sealed record PreparedRetrievalContext(IRetrievalContext Context, string Body, IReadOnlyList<Source> Sources, SourcePassage? Passage)
+{
+    /// <summary>
+    /// Writes what the AI is told about the context, headed by its number.
+    /// </summary>
+    /// <param name="index">The number of the context among all of them, or null when it stands alone.</param>
+    /// <param name="numTotalRetrievalContexts">How many contexts there are, or null when that is unknown.</param>
+    /// <returns>The context as Markdown, ending with an empty line to set it apart from the next one.</returns>
+    public string ToMarkdown(int? index = null, int? numTotalRetrievalContexts = null)
+    {
+        var sb = new StringBuilder();
+        switch (index)
+        {
+            case > 0 when numTotalRetrievalContexts is null:
+                sb.AppendLine($"# Retrieval context {index}");
+                break;
+
+            case > 0 when numTotalRetrievalContexts > 0:
+                sb.AppendLine($"# Retrieval context {index} of {numTotalRetrievalContexts}");
+                break;
+
+            default:
+                sb.AppendLine("# Retrieval context");
+                break;
+        }
+
+        sb.Append(this.Body);
+        sb.AppendLine();
+        return sb.ToString();
+    }
+}