Added mailboxes as local data sources (#1022)

app/MindWork AI Studio/Tools/Mail/MailboxConnectionException.cs

@@ -0,0 +1,17 @@
+namespace AIStudio.Tools.Mail;
+
+/// <summary>
+/// A connection to the IMAP server of a mailbox failed, for the reason its failure code names.
+/// </summary>
+/// <remarks>
+/// The message is meant for developers and names neither the user nor the server. The inner
+/// exception may well do so, since servers tend to repeat the username in their answers. Log the
+/// failure code and the type of the inner exception, never its message.
+/// </remarks>
+public sealed class MailboxConnectionException(MailboxConnectionFailure failure, string message, Exception? innerException = null) : Exception(message, innerException)
+{
+    /// <summary>
+    /// Why the connection failed.
+    /// </summary>
+    public MailboxConnectionFailure Failure { get; } = failure;
+}