Record why the directory dialog reports from its worker thread

app/MindWork AI Studio/Dialogs/DataSourceLocalDirectoryInfoDialog.razor.cs

@@ -60,6 +60,22 @@ public partial class DataSourceLocalDirectoryInfoDialog : MSGComponentBase
 
     private bool IsDirectoryAvailable => this.directoryInfo.Exists;
 
+    /// <summary>
+    /// Takes the next file which the directory scan found.
+    /// </summary>
+    /// <remarks>
+    /// This runs on the scan's own thread, and it does so deliberately, although the scan asks its
+    /// callers to reach for a dispatcher. That request is about updating the UI, and none of these
+    /// callbacks does: they write fields and nothing else.<br/><br/>
+    /// Why that holds is worth writing down, because the code does not show it. The string builder
+    /// has exactly one writer -- this method, on that one thread -- and nobody else ever reads it.
+    /// What the renderer reads is the text field beside it, and assigning a string reference is
+    /// atomic, so a render sees the whole previous text or the whole new one, never half of either.
+    /// Building that text anew costs little, because the scan stops reporting files once it has
+    /// reported a hundred. And a render happens only when the refresh timer ticks, which goes
+    /// through the dispatcher, so a reading taken a moment too early is replaced 1.6 seconds later
+    /// anyway.
+    /// </remarks>
     private void UpdateFileList(string file)
     {
         this.directoryFiles.Append("- ");
@@ -67,13 +83,38 @@ public partial class DataSourceLocalDirectoryInfoDialog : MSGComponentBase
         this.directoryFilesText = this.directoryFiles.ToString();
     }
 
+    /// <summary>
+    /// Takes the size which the directory scan has added up so far.
+    /// </summary>
+    /// <remarks>
+    /// Two threads call this, but never at the same time: the scan reports its progress from its
+    /// own thread, and the final figure follows once that thread has finished. A long is written in
+    /// one piece on all six targets we ship, which are 64 bit throughout, and the renderer reads it
+    /// only when the refresh timer ticks. The remark on the file list carries the reasoning these
+    /// callbacks share.
+    /// </remarks>
     private void UpdateDirectorySize(long size)
     {
         this.directorySizeBytes = size;
     }
 
+    /// <summary>
+    /// Takes the number of files which the directory scan has counted so far.
+    /// </summary>
+    /// <remarks>
+    /// Reported from the same two threads as the size above, and safe for the same reason.
+    /// </remarks>
     private void UpdateDirectoryFiles(long numFiles) => this.directorySizeNumFiles = numFiles;
 
+    /// <summary>
+    /// Takes the news that the directory scan has finished.
+    /// </summary>
+    /// <remarks>
+    /// This one, unlike the three above, does not run on the scan's thread. The scan invokes it
+    /// after awaiting its worker, and that continuation returns to the dispatcher this dialog was
+    /// initialized on. Stopping the timer and asking for a render from here is therefore no
+    /// different from doing either in a lifecycle method.
+    /// </remarks>
     private void DirectoryOperationDone()
     {
         this.refreshTimer.Stop();