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

app/MindWork AI Studio/Assistants/GrammarSpelling/AssistantGrammarSpelling.razor.cs

@@ -12,6 +12,9 @@ public partial class AssistantGrammarSpelling : AssistantBaseCore<SettingsDialog
     
     protected override string Description => T("Check the grammar and spelling of a text.");
     
+    // The prompt of this assistant forbids explanations, so the chat gets a prompt of its own, which keeps the rules of the language:
+    protected override ChatSystemPromptChoice ChatSystemPrompt => ChatSystemPromptChoice.Custom(this.CreateChatSystemPrompt);
+
     protected override string SystemPrompt => 
         $"""
         You are an expert in languages and their rules. For example, you know how US and UK English or German in
@@ -21,6 +24,21 @@ public partial class AssistantGrammarSpelling : AssistantBaseCore<SettingsDialog
         Your response includes only the corrected text. Do not explain your changes. If no changes are needed,
         you return the text unchanged.
         """;
+
+    /// <summary>
+    /// Creates the system prompt of a chat which continues a check of spelling and grammar, for follow-up questions about it.
+    /// </summary>
+    private string CreateChatSystemPrompt() =>
+        $"""
+        You are an expert in languages and their rules. For example, you know how US and UK English or German in
+        Germany and German in Austria differ. The user had a text checked for spelling and grammar according to the
+        rules of {this.SystemPromptLanguage()}: the conversation so far holds the text and its corrected version.
+        Now you answer the user's follow-up questions about the corrections, e.g., which rule applies or why a sentence
+        changed, and you check further texts or revise the corrected text when the user asks for it. When you correct a
+        text, you correct only its spelling and grammar and keep its wording, unless the user asks otherwise.
+
+        Answer questions in the language the user writes in.
+        """;
     
     protected override bool AllowProfiles => false;