Added the exact token count for the OpenAI Responses API

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

@@ -10,4 +10,15 @@ namespace AIStudio.Provider.OpenAI;
 /// </remarks>
 /// <param name="Type">The type of the stream event.</param>
 /// <param name="Response">The response as a non-streamed call would have returned it.</param>
-public sealed record ResponsesCompletedStreamLine(string Type, ResponsesResponse? Response);
+public sealed record ResponsesCompletedStreamLine(string Type, ResponsesResponse? Response)
+{
+    /// <summary>
+    /// States what the request of this call carried, as far as it can be believed.
+    /// </summary>
+    /// <remarks>
+    /// The one way from the wire to a usage, shared by the plain text path and the tool calling
+    /// path, so that what counts as believable is decided in a single place.
+    /// </remarks>
+    /// <returns>The usage, or TokenUsage.UNKNOWN when the line states nothing usable.</returns>
+    public TokenUsage GetUsage() => this.Response?.GetUsage() ?? TokenUsage.UNKNOWN;
+}