Generated the JSON contracts of providers, the runtime, and services at compile time (#1150)

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

@@ -7,6 +7,14 @@ namespace AIStudio.Provider.OpenAI;
 /// <param name="Delta">The delta text of the choice.</param>
 public record ChatCompletionChoice(int Index, ChatCompletionDelta Delta)
 {
+    //
+    // The properties of the parameters, declared again to be settable. The source generation of System.Text.Json
+    // sets every init-only property while it creates the object, also one missing in the JSON, so its value from
+    // the parameterless constructor would get lost. Keep them first and in the order of the parameters:
+    //
+    public int Index { get; set; } = Index;
+    public ChatCompletionDelta Delta { get; set; } = Delta;
+
     public ChatCompletionChoice() : this(0, new())
     {
     }