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

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

@@ -7,6 +7,15 @@ namespace AIStudio.Provider.OpenAI;
 /// <param name="Role">The role of the message.</param>
 public record MultimodalMessage(List<ISubContent> Content, string Role) : IMessage<List<ISubContent>>
 {
+    //
+    // 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, which is
+    // the order they get written in:
+    //
+    public List<ISubContent> Content { get; set; } = Content;
+    public string Role { get; set; } = Role;
+
     public MultimodalMessage() : this([], string.Empty)
     {
     }