Pair buffered document content with its own token count

app/MindWork AI Studio/Tools/Slide.cs

@@ -5,6 +5,16 @@ public sealed class Slide
     public bool Delivered { get; set; }
 
     public int Position { get; init; }
-    
+
     public List<ISlideContent> Content { get; } = new();
+
+    /// <summary>
+    /// The number of tokens of everything this slide holds, or null when it is unknown.
+    /// </summary>
+    /// <remarks>
+    /// A slide grows across several stream events, so its count grows with it. It becomes unknown
+    /// as soon as an image is embedded: the runtime counted the text of the slide, and a data URI
+    /// is orders of magnitude larger than that.
+    /// </remarks>
+    public int? TokenCount { get; set; }
 }