Indexed large data sources in steps so the others get their turn (#1052)

app/MindWork AI Studio/Tools/Services/Indexing/MailboxIndexer.Mails.cs

@@ -69,6 +69,17 @@ internal sealed partial class MailboxIndexer
             return;
         }
 
+        //
+        // A mail which failed during an earlier step of this sync waits for the next sync, unless
+        // it changed since. Asked only here: the mail counts as encountered all the same, and one
+        // which merely moved was linked above.
+        //
+        if (progress.SkipIfFailedEarlierInPass(key, mailHash))
+        {
+            progress.Publish();
+            return;
+        }
+
         //
         // Named after the subject as the server delivered it. The name is for the user alone, who
         // reads it on the embeddings page as in any mail program. A model only ever gets to read