Carry provider sources through the Chat Completions tool rounds

app/MindWork AI Studio/Provider/OpenAI/ChatCompletionStreamPart.cs

@@ -4,15 +4,16 @@ namespace AIStudio.Provider.OpenAI;
 /// What one line of a streamed Chat Completions answer has to show to the user.
 /// </summary>
 /// <param name="TextDelta">The text this line carried, empty when it carried none.</param>
-public readonly record struct ChatCompletionStreamPart(string TextDelta)
+/// <param name="Sources">The sources this line announced, empty when it announced none.</param>
+public readonly record struct ChatCompletionStreamPart(string TextDelta, IList<ISource> Sources)
 {
     /// <summary>
     /// The part of a line which says nothing to the user, such as a fragment of a tool call.
     /// </summary>
-    public static ChatCompletionStreamPart Nothing => new(string.Empty);
+    public static ChatCompletionStreamPart Nothing => new(string.Empty, []);
     
     /// <summary>
     /// Whether this part has anything to show at all.
     /// </summary>
-    public bool HasContent => this.TextDelta.Length > 0;
+    public bool HasContent => this.TextDelta.Length > 0 || this.Sources.Count > 0;
 }