diff --git a/JitHub.WinUI/Services/CodeViewer/RepoFileCacheService.cs b/JitHub.WinUI/Services/CodeViewer/RepoFileCacheService.cs
index bc9f301..95713c8 100644
--- a/JitHub.WinUI/Services/CodeViewer/RepoFileCacheService.cs
+++ b/JitHub.WinUI/Services/CodeViewer/RepoFileCacheService.cs
@@ -49,7 +49,7 @@ public RepoFileCacheService(int memMaxEntries, long memMaxBytes, long diskMaxByt
         _diskMaxBytes = diskMaxBytes;
         _ttl = ttl;
 
-        _diskRoot = Path.Combine(ApplicationData.Current.LocalCacheFolder.Path, "RepoFileCache");
+        _diskRoot = GetDefaultDiskRoot();
         Directory.CreateDirectory(_diskRoot);
 
         // Background startup purge — do not block the constructor.
@@ -73,6 +73,22 @@ internal RepoFileCacheService(
 
     // ── Public API ───────────────────────────────────────────────────────────
 
+    private static string GetDefaultDiskRoot()
+    {
+        try
+        {
+            return Path.Combine(ApplicationData.Current.LocalCacheFolder.Path, "RepoFileCache");
+        }
+        catch (InvalidOperationException)
+        {
+            string localAppData = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
+            if (string.IsNullOrWhiteSpace(localAppData))
+                localAppData = Path.GetTempPath();
+
+            return Path.Combine(localAppData, "JitHub", "RepoFileCache");
+        }
+    }
+
     public bool TryGet(RepoFileCacheKey key, out RepoFileCacheEntry entry)
     {
         string mk = MemKey(key);
diff --git a/MarkdownRenderer/MarkdownRenderer/Controls/MarkdownRendererControl.cs b/MarkdownRenderer/MarkdownRenderer/Controls/MarkdownRendererControl.cs
index b355650..2a6ee5c 100644
--- a/MarkdownRenderer/MarkdownRenderer/Controls/MarkdownRendererControl.cs
+++ b/MarkdownRenderer/MarkdownRenderer/Controls/MarkdownRendererControl.cs
@@ -2138,24 +2138,57 @@ private bool EnsureLazyLayoutForViewport()
         if (snapshot is null || !snapshot.IsLazyLayoutEnabled || _scroll is null)
             return false;
 
-        var anchor = CaptureScrollAnchor(snapshot, _scroll.VerticalOffset);
-        var commit = snapshot.EnsureMeasuredViewport(
+        var band = LazyLayoutBand.FromViewport(
             _scroll.VerticalOffset,
             _scroll.ViewportHeight > 0 ? _scroll.ViewportHeight : Math.Max(ActualHeight, 600),
-            LazyLayoutOverscanPx,
-            CancellationToken.None);
+            LazyLayoutOverscanPx);
 
+        return EnsureLazyLayoutForBand(snapshot, band, preserveScrollAnchor: true, invalidateCanvas: true);
+    }
+
+    private bool EnsureLazyLayoutForPaintRegion(Rect region)
+    {
+        var snapshot = _snapshot;
+        if (snapshot is null || !snapshot.IsLazyLayoutEnabled)
+            return false;
+
+        var band = LazyLayoutBand.FromViewport(region.Top, region.Height, LazyLayoutOverscanPx);
+        return EnsureLazyLayoutForBand(snapshot, band, preserveScrollAnchor: _scroll is not null, invalidateCanvas: false);
+    }
+
+    private bool EnsureLazyLayoutForBand(
+        LayoutSnapshot snapshot,
+        LazyLayoutBand band,
+        bool preserveScrollAnchor,
+        bool invalidateCanvas)
+    {
+        (int BlockIndex, double OffsetFromTop)? anchor = null;
+        if (preserveScrollAnchor && _scroll is not null)
+            anchor = CaptureScrollAnchor(snapshot, _scroll.VerticalOffset);
+
+        var commit = snapshot.EnsureMeasuredBand(band, CancellationToken.None);
         if (!commit.Changed)
             return false;
 
+        ApplyLazyLayoutCommit(snapshot, anchor, invalidateCanvas);
+        return true;
+    }
+
+    private void ApplyLazyLayoutCommit(
+        LayoutSnapshot snapshot,
+        (int BlockIndex, double OffsetFromTop)? scrollAnchor,
+        bool invalidateCanvas)
+    {
         ApplySnapshotSize(snapshot);
-        RestoreScrollAnchor(snapshot, anchor);
+        RestoreScrollAnchor(snapshot, scrollAnchor);
         RebuildRealizationPlans(snapshot, preserveRealized: true);
         _focusableItems = snapshot.CollectFocusableItems();
+        RealizeVisibleEmbeds();
+        ScheduleVisibleCodeBlockHighlighting();
         UpdateSelectionAdornerViewport();
         UpdateFocusRing();
-        _canvas?.Invalidate();
-        return true;
+        if (invalidateCanvas)
+            _canvas?.Invalidate();
     }
 
     private void DerealizeAllEmbeds()
@@ -2482,6 +2515,9 @@ private void OnRegionsInvalidated(CanvasVirtualControl sender, CanvasRegionsInva
                     "region", regionCount, region.X, region.Y, region.Width, region.Height);
             try
             {
+                // The tile itself is the authoritative paint band; the ScrollViewer
+                // viewport can lag behind CanvasVirtualControl's region requests.
+                EnsureLazyLayoutForPaintRegion(region);
                 using var ds = sender.CreateDrawingSession(region);
                 // Clear to the theme-appropriate background color so that switching between
                 // light and dark mode (or any theme change) fully overwrites old tile content.
diff --git a/MarkdownRenderer/MarkdownRenderer/Layout/Boxes/InlineContainerBox.cs b/MarkdownRenderer/MarkdownRenderer/Layout/Boxes/InlineContainerBox.cs
index 62c3e9b..7ac6484 100644
--- a/MarkdownRenderer/MarkdownRenderer/Layout/Boxes/InlineContainerBox.cs
+++ b/MarkdownRenderer/MarkdownRenderer/Layout/Boxes/InlineContainerBox.cs
@@ -483,7 +483,15 @@ internal IEnumerable<Rect> GetBufferRangeLineRects(int from, int length)
         int rangeEnd = from + length;
         int lineStart = 0;
         double y = 0;
-        foreach (var metric in _layout.LineMetrics)
+        var lineMetrics = TryGetLineMetrics();
+        if (lineMetrics is null)
+        {
+            foreach (var rect in GetBufferRangeRects(from, length))
+                yield return rect;
+            yield break;
+        }
+
+        foreach (var metric in lineMetrics)
         {
             int charCount = Math.Max(0, metric.CharacterCount);
             int lineEnd = lineStart + charCount;
@@ -557,7 +565,7 @@ public void PaintLinkStateForeground(CanvasDrawingSession ds, LinkRun link, bool
             if (regions is null)
                 return;
 
-            var lineMetrics = _layout.LineMetrics;
+            var lineMetrics = TryGetLineMetrics();
             foreach (var r in regions)
             {
                 var rect = new Rect(
@@ -1124,9 +1132,10 @@ private void DrawDecorations(CanvasDrawingSession ds, float baseX, float baseY)
     private void DrawDecorations(CanvasDrawingSession ds, float baseX, float baseY, Color? overrideColor)
     {
         if (_layout is null) return;
-        var lineMetrics = _layout.LineMetrics;
 
         int cumulative = 0;
+        CanvasLineMetrics[]? lineMetrics = null;
+        bool lineMetricsAttempted = false;
         foreach (var run in _runs)
         {
             int len = run.Text.Length;
@@ -1145,6 +1154,11 @@ private void DrawDecorations(CanvasDrawingSession ds, float baseX, float baseY,
 
             if (rs.Underline || rs.Strikethrough)
             {
+                if (!lineMetricsAttempted)
+                {
+                    lineMetrics = TryGetLineMetrics();
+                    lineMetricsAttempted = true;
+                }
                 var regions = _layout.GetCharacterRegions(cumulative, len);
                 if (regions is null) { cumulative += len; continue; } // Win2D can return null on DirectWrite errors
                 foreach (var r in regions)
@@ -1160,7 +1174,7 @@ private static void DrawRunDecorations(
         CanvasDrawingSession ds,
         float baseX,
         float baseY,
-        CanvasLineMetrics[] lineMetrics,
+        CanvasLineMetrics[]? lineMetrics,
         CanvasTextLayoutRegion region,
         InlineRun run,
         ElementStyle style,
@@ -1240,8 +1254,25 @@ private void DrawRunBackgrounds(CanvasDrawingSession ds, float baseX, float base
         }
     }
 
-    private static CanvasLineMetrics FindLineMetrics(CanvasLineMetrics[] metrics, CanvasTextLayoutRegion region)
+    private CanvasLineMetrics[]? TryGetLineMetrics()
     {
+        try
+        {
+            return _layout?.LineMetrics;
+        }
+        catch (NotSupportedException)
+        {
+            // Some WinRT/Release projections cannot marshal CanvasLineMetrics.
+            // Text still renders; decoration placement can use region bounds.
+            return null;
+        }
+    }
+
+    private static CanvasLineMetrics FindLineMetrics(CanvasLineMetrics[]? metrics, CanvasTextLayoutRegion region)
+    {
+        if (metrics is null || metrics.Length == 0)
+            return default;
+
         int idx = (int)region.CharacterIndex;
         int run = 0;
         foreach (var m in metrics)