Added mailboxes as local data sources (#1022)

app/MindWork AI Studio/Tools/Databases/IndexStore/MailboxAuthFailure.cs

@@ -0,0 +1,29 @@
+namespace AIStudio.Tools.Databases.IndexStore;
+
+/// <summary>
+/// A sign-in the server of a mailbox refused.
+/// </summary>
+/// <param name="FailedAtUtc">When the server refused the sign-in.</param>
+/// <param name="FailureMessage">What the server answered, empty when it gave no reason.</param>
+public sealed record MailboxAuthFailure(DateTimeOffset FailedAtUtc, string FailureMessage)
+{
+    /// <summary>
+    /// How much of the answer of the server is kept. The reason is in the first sentence, if at all.
+    /// </summary>
+    public const int MAX_FAILURE_MESSAGE_LENGTH = 500;
+
+    /// <summary>
+    /// Records a sign-in the server refused just now, together with what it answered.
+    /// </summary>
+    /// <remarks>
+    /// The answer often says why, e.g., that the provider requires an app password. It may name
+    /// the user as well, which is why it is kept for the settings of the mailbox and never logged.
+    /// </remarks>
+    /// <param name="serverAnswer">What the server answered.</param>
+    /// <returns>The refused sign-in.</returns>
+    public static MailboxAuthFailure FromServerAnswer(string serverAnswer)
+    {
+        var trimmedAnswer = serverAnswer.Trim();
+        return new(DateTimeOffset.UtcNow, trimmedAnswer.Length > MAX_FAILURE_MESSAGE_LENGTH ? trimmedAnswer[..MAX_FAILURE_MESSAGE_LENGTH] : trimmedAnswer);
+    }
+}