Fixed and improved the system prompt of chats started from assistants (#1172)

app/MindWork AI Studio/Chat/ChatSystemPromptOrigin.cs

@@ -0,0 +1,25 @@
+using AIStudio.Assistants;
+
+namespace AIStudio.Chat;
+
+/// <summary>
+/// Which assistant chose the system prompt of a chat, and how.
+/// </summary>
+/// <remarks>
+/// Stored with a chat which continues the conversation of an assistant, so that the dialog showing the
+/// system prompt can name the assistant, and tell the prompt of the assistant apart from a prompt the
+/// assistant wrote for the chat. A chat without it got its prompt elsewhere: from AI Studio, from a
+/// chat template, or from a version of AI Studio before v26.11.1.
+/// </remarks>
+public sealed record ChatSystemPromptOrigin
+{
+    /// <summary>
+    /// Whether the chat got the prompt of the assistant or a prompt the assistant wrote for the chat.
+    /// </summary>
+    public ChatSystemPromptSource Source { get; set; } = ChatSystemPromptSource.ASSISTANT;
+
+    /// <summary>
+    /// The name of the assistant, as AI Studio showed it when the chat started.
+    /// </summary>
+    public string AssistantName { get; set; } = string.Empty;
+}