Added mailboxes as local data sources (#1022)

app/MindWork AI Studio/Chat/StringExtension.cs

@@ -15,4 +15,24 @@ public static class StringExtensions
         
         return input[(endIndex + CLOSE_TAG.Length)..];
     }
+
+    /// <summary>
+    /// Shortens a text to the given number of characters, and marks the cut with three dots.
+    /// </summary>
+    /// <remarks>
+    /// Never cuts between the two halves of a surrogate pair, which no JSON writer takes.<br/><br/>
+    /// Takes and returns a string rather than a span on purpose: most texts are short enough, and
+    /// those come back as the very same instance. Only a text which is cut costs one new string.
+    /// </remarks>
+    /// <param name="text">The text.</param>
+    /// <param name="maxCharacters">How many characters of the text to keep at most, the dots not counted.</param>
+    /// <returns>The text as it was when it is short enough, otherwise its beginning followed by three dots.</returns>
+    public static string Shorten(this string text, int maxCharacters)
+    {
+        if (text.Length <= maxCharacters)
+            return text;
+
+        var end = char.IsHighSurrogate(text[maxCharacters - 1]) ? maxCharacters - 1 : maxCharacters;
+        return string.Concat(text.AsSpan(0, end).TrimEnd(), "...");
+    }
 }