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

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

@@ -0,0 +1,36 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace AIStudio.Provider.OpenAI;
+
+/// <summary>
+/// What one choice of a streamed Chat Completions answer adds in this line.
+/// </summary>
+/// <remarks>
+/// This is the delta of the plain text path plus the two fields that path has no use for: the
+/// reasoning some providers send alongside, and the tool calls the model asks for.
+/// </remarks>
+public sealed record ChatCompletionStreamDelta
+{
+    /// <summary>
+    /// The content as it arrived: a string for most providers, a list of parts for some.
+    /// </summary>
+    [JsonPropertyName("content")]
+    public JsonElement? RawContent { get; init; }
+
+    /// <summary>
+    /// The text of this fragment, whichever shape it arrived in.
+    /// </summary>
+    [JsonIgnore]
+    public string Content => ChatCompletionContent.GetText(this.RawContent) ?? string.Empty;
+
+    /// <summary>
+    /// The reasoning text some providers stream next to the answer.
+    /// </summary>
+    public string? ReasoningContent { get; init; }
+
+    /// <summary>
+    /// The fragments of the tool calls the model is asking for.
+    /// </summary>
+    public IList<ChatCompletionToolCallDelta?>? ToolCalls { get; init; }
+}