Stream the answers again whenever tools are in play (#986)

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

@@ -0,0 +1,60 @@
+using System.Text.Json;
+
+namespace AIStudio.Provider.OpenAI;
+
+/// <summary>
+/// Reads the sources a provider puts into its Chat Completions stream.
+/// </summary>
+/// <remarks>
+/// Where those sit differs per provider: OpenAI announces them on annotation lines of their own,
+/// Perplexity puts its search results into the very line that carries the text. The plain text
+/// path reads both through the provider's own stream line types, and so does this -- otherwise
+/// the tool calling rounds would be the one place where a citation link goes missing.
+/// </remarks>
+public static class ChatCompletionSourceReader
+{
+    private const string DONE = "[DONE]";
+    
+    /// <summary>
+    /// Reads whatever sources one line of the stream announced.
+    /// </summary>
+    /// <param name="serverSentEvent">The event to read.</param>
+    /// <typeparam name="TDelta">The provider's delta stream line type.</typeparam>
+    /// <typeparam name="TAnnotation">The provider's annotation stream line type.</typeparam>
+    /// <returns>The sources of this line, empty when it announced none.</returns>
+    public static IList<ISource> Read<TDelta, TAnnotation>(ServerSentEvent serverSentEvent)
+        where TDelta : IResponseStreamLine
+        where TAnnotation : IAnnotationStreamLine
+    {
+        if (serverSentEvent.Data.Length is 0 || serverSentEvent.Data is DONE)
+            return [];
+
+        //
+        // The same split the plain text path makes, and for the same reason: a line is either an
+        // annotation line or a delta line, and reading it as both would count its sources twice.
+        //
+        var annotationSupported = typeof(TAnnotation) != typeof(NoResponsesAnnotationStreamLine) && typeof(TAnnotation) != typeof(NoChatCompletionAnnotationStreamLine);
+        if (annotationSupported && serverSentEvent.Line.Contains("""
+                                                                 "annotations":[
+                                                                 """, StringComparison.InvariantCulture))
+        {
+            var annotationLine = TryDeserialize<TAnnotation>(serverSentEvent.Data);
+            return annotationLine is not null && annotationLine.ContainsSources() ? annotationLine.GetSources() : [];
+        }
+
+        var deltaLine = TryDeserialize<TDelta>(serverSentEvent.Data);
+        return deltaLine is not null && deltaLine.ContainsSources() ? deltaLine.GetSources() : [];
+    }
+    
+    private static T? TryDeserialize<T>(string json)
+    {
+        try
+        {
+            return JsonSerializer.Deserialize<T>(json, ProviderJsonOptions.OPTIONS);
+        }
+        catch (JsonException)
+        {
+            return default;
+        }
+    }
+}