Show folder names immediately and refresh stale index sizes without walking the whole drive.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/Explorer.Application/FolderStatusText.cs

@@ -0,0 +1,73 @@
+using Explorer.Domain;
+
+namespace Explorer.Application;
+
+public static class FolderStatusText
+{
+    public static string Format(IEnumerable<FileSystemItem> folderItems, IEnumerable<FileSystemItem> selectedItems)
+    {
+        var selected = selectedItems as IReadOnlyCollection<FileSystemItem> ?? selectedItems.ToList();
+        var isSelection = selected.Count > 0;
+        var totals = Measure(isSelection ? selected : folderItems);
+        var noun = totals.Count == 1 ? "item" : "items";
+        var prefix = isSelection
+            ? $"{totals.Count:N0} {noun} selected"
+            : $"{totals.Count:N0} {noun}";
+        if (!ShouldShowSize(totals))
+        {
+            return prefix;
+        }
+
+        return $"{prefix}  ·  {FormatSize(totals.KnownBytes)}";
+    }
+
+    public static FolderStatusTotals Measure(IEnumerable<FileSystemItem> items)
+    {
+        var count = 0;
+        var files = 0;
+        var knownBytes = 0L;
+        var hasKnownSize = false;
+        foreach (var item in items)
+        {
+            count++;
+            if (!item.IsDirectory)
+            {
+                files++;
+            }
+
+            if (item.SizeKnowledge == SizeKnowledge.Unknown)
+            {
+                continue;
+            }
+
+            knownBytes += Math.Max(0, item.SizeBytes);
+            hasKnownSize = true;
+        }
+
+        return new FolderStatusTotals(count, files, knownBytes, hasKnownSize);
+    }
+
+    private static bool ShouldShowSize(FolderStatusTotals totals)
+        => totals.HasKnownSize && (totals.KnownBytes > 0 || totals.Files > 0);
+
+    private static string FormatSize(long bytes)
+    {
+        if (bytes < 0)
+        {
+            return string.Empty;
+        }
+
+        string[] units = ["B", "KB", "MB", "GB", "TB", "PB"];
+        double value = bytes;
+        var unit = 0;
+        while (value >= 1024 && unit < units.Length - 1)
+        {
+            value /= 1024;
+            unit++;
+        }
+
+        return unit == 0 ? $"{bytes} B" : $"{value:0.##} {units[unit]}";
+    }
+}
+
+public readonly record struct FolderStatusTotals(int Count, int Files, long KnownBytes, bool HasKnownSize);