Fix leading divider rendering for boxes without title area

src/DemaConsulting.Rendering.Skia/SkiaRasterRenderer.cs

@@ -508,14 +508,22 @@
         var scale = (float)options.Scale;
 
         // Compartments start below the title area (keyword + label), computed via shared metrics
+        var hasTitleArea = box.Label != null || box.Keyword != null;
         var labelAreaHeight = BoxMetrics.TitleAreaHeight(theme, box.Label != null, box.Keyword != null);
         var compartmentY = ResolveTitleAreaTop(box, theme) + box.ContentInsetTop + labelAreaHeight;
 
+        var isFirstCompartment = true;
         foreach (var compartment in box.Compartments)
         {
-            // Draw a full-width horizontal divider at the top of this compartment
-            using (var divPaint = new SKPaint())
+            // The divider above the first compartment only has something to separate from when a
+            // keyword/label title area precedes it. With no title area, this divider would sit
+            // exactly on the box's own top edge — redundant for a plain rectangle (the two lines
+            // coincide) but a genuine visible defect for shapes whose top edge isn't a plain
+            // straight line across the full width (e.g. Note's folded corner cutout), where the
+            // full-width divider ignores the cut and renders as a stray line past the fold.
+            if (!isFirstCompartment || hasTitleArea)
             {
+                using var divPaint = new SKPaint();
                 divPaint.Color = strokeColor;
                 divPaint.Style = SKPaintStyle.Stroke;
                 divPaint.StrokeWidth = (float)theme.StrokeWidth * scale;
@@ -527,6 +535,8 @@
                     divPaint);
             }
 
+            isFirstCompartment = false;
+
             // Draw the optional bold compartment title
             if (compartment.Title != null)
             {
@@ -568,7 +578,7 @@
     /// <param name="canvas">Canvas to draw on.</param>
     /// <param name="line">Line node to render.</param>
     /// <param name="options">Render options providing theme and scale.</param>
     private static void RenderLine(SKCanvas canvas, LayoutLine line, RenderOptions options)
     {
         // Lines with fewer than 2 waypoints cannot be drawn
         if (line.Waypoints.Count < 2)
@@ -918,7 +928,7 @@
     /// <param name="vertex">The tip-relative marker vertex in notation units.</param>
     /// <param name="scale">Uniform scale factor.</param>
     /// <returns>The mapped canvas point.</returns>
     private static SKPoint MarkerPoint(
         float tipX, float tipY, float dx, float dy, float px, float py, MarkerVertex vertex, float scale)
     {
         var along = (float)vertex.Along;
@@ -1077,7 +1087,7 @@
     /// Builds the triangle marker path from <see cref="NotationMetrics.TriangleVertices"/>, optionally
     /// closing the base edge (closed for the hollow/filled triangle, open for the chevron).
     /// </summary>
     private static SKPath TrianglePath(
         float tipX, float tipY, float dx, float dy, float px, float py, float scale, bool close)
     {
         var vertices = NotationMetrics.TriangleVertices();

src/DemaConsulting.Rendering.Svg/SvgRenderer.cs

@@ -597,15 +597,28 @@
     private static void RenderBoxCompartments(StringBuilder sb, LayoutBox box, Theme theme, double scale)
     {
         // Compartments start below the title area (keyword + label), computed via shared metrics
+        var hasTitleArea = box.Label != null || box.Keyword != null;
         var labelAreaHeight = BoxMetrics.TitleAreaHeight(theme, box.Label != null, box.Keyword != null);
         var compartmentY = ResolveTitleAreaTop(box, theme) + box.ContentInsetTop + labelAreaHeight;
 
+        var isFirstCompartment = true;
         foreach (var compartment in box.Compartments)
         {
-            // Full-width horizontal divider at the top of this compartment
-            sb.Append(CultureInfo.InvariantCulture,
-                $"""  <line x1="{F(box.X * scale)}" y1="{F(compartmentY * scale)}" x2="{F((box.X + box.Width) * scale)}" y2="{F(compartmentY * scale)}" stroke="{theme.StrokeColor}" stroke-width="{F(theme.StrokeWidth)}"/>""");
-            sb.AppendLine();
+            // The divider above the first compartment only has something to separate from when a
+            // keyword/label title area precedes it. With no title area, this divider would sit
+            // exactly on the box's own top edge — redundant for a plain rectangle (the two lines
+            // coincide) but a genuine visible defect for shapes whose top edge isn't a plain
+            // straight line across the full width (e.g. Note's folded corner cutout), where the
+            // full-width divider ignores the cut and renders as a stray line past the fold.
+            if (!isFirstCompartment || hasTitleArea)
+            {
+                // Full-width horizontal divider at the top of this compartment
+                sb.Append(CultureInfo.InvariantCulture,
+                    $"""  <line x1="{F(box.X * scale)}" y1="{F(compartmentY * scale)}" x2="{F((box.X + box.Width) * scale)}" y2="{F(compartmentY * scale)}" stroke="{theme.StrokeColor}" stroke-width="{F(theme.StrokeWidth)}"/>""");
+                sb.AppendLine();
+            }
+
+            isFirstCompartment = false;
 
             // Draw optional bold compartment title
             if (compartment.Title != null)
@@ -783,7 +796,7 @@
     /// <param name="sourceEnd">End-marker style at the first waypoint (source endpoint).</param>
     /// <param name="targetEnd">End-marker style at the last waypoint (target endpoint).</param>
     /// <returns>SVG path data string starting with <c>M</c>.</returns>
     private static string BuildLinePath(
         IReadOnlyList<Point2D> waypoints,
         double cornerRadius,
         double scale,

test/DemaConsulting.Rendering.Skia.Tests/SkiaPortAndContentInsetTests.cs

@@ -217,6 +217,55 @@ private static int RightmostForegroundX(SKBitmap bitmap, SKColor background, int
         return -1;
     }
 
+    /// <summary>
+    ///     Proves that rendering a Note-shaped box with a compartment and no Label/Keyword does not
+    ///     draw a stray divider line protruding past the note's folded-corner cutout. With no title
+    ///     area, the first compartment's divider would land exactly on the box's own top edge; for a
+    ///     plain rectangle that's an invisible duplicate, but for Note it must not extend past the
+    ///     diagonal fold (from xFold to the right edge) as a visible artifact.
+    /// </summary>
+    [Fact]
+    public void PngRenderer_Render_NoteBoxWithCompartmentAndNoTitle_NoStrayLinePastFold()
+    {
+        // Arrange: a Note-shaped box with a compartment but no Label/Keyword
+        var renderer = new PngRenderer();
+        var compartment = new LayoutCompartment(null, ["Some body text"]);
+        var box = new LayoutBox(10, 10, 150, 80, null, 0, BoxShape.Note, [compartment], []);
+        var options = new RenderOptions(Themes.Light);
+        var background = SKColor.Parse(Themes.Light.BackgroundColor);
+
+        using var stream = new MemoryStream();
+        renderer.Render(new LayoutTree(200, 120, [box]), options, stream);
+        stream.Position = 0;
+        using var data = SKData.Create(stream);
+        using var bitmap = SKBitmap.Decode(data);
+
+        // Compute the fold's scaled x-position (matching RenderNotePng's own geometry) and scan a
+        // vertical band just below the box's top edge. The divider (a ~1.5px stroke) can land
+        // partially on adjacent rows once anti-aliased, so a single row risked missing or flaking
+        // on the regression; scanning several rows makes the check reliable. The diagonal fold edge
+        // has a 1:1 slope (rise == run == fold size) starting at (xFold, yTop), so the scan's xStart
+        // is offset past where that diagonal (plus its anti-aliasing) could reach within the band,
+        // ensuring only a genuine stray horizontal divider - not the legitimate fold edge - would be
+        // detected.
+        var fold = Math.Min(Math.Min(box.Width, box.Height) * NotationMetrics.NoteFoldFraction, NotationMetrics.NoteFoldMaxSize);
+        var scale = options.Scale;
+        var xFold = (int)((box.X + box.Width - fold) * scale);
+        var yTop = (int)(box.Y * scale);
+        const int bandHeight = 4;
+        const int diagonalClearance = 3;
+
+        var rightmost = RightmostForegroundX(
+            bitmap,
+            background,
+            yStart: yTop,
+            yEnd: yTop + bandHeight,
+            xStart: xFold + bandHeight + diagonalClearance);
+
+        // Assert: no stray foreground pixel found past the fold at the top edge
+        Assert.Equal(-1, rightmost);
+    }
+
     /// <summary>
     ///     Proves that when 3+ parallel labeled connectors force the label placer to nudge labels
     ///     downward to avoid collisions, the raster renderer grows the bitmap (rather than sizing it

test/DemaConsulting.Rendering.Svg.Tests/SvgRendererPortedTests.cs

@@ -284,6 +284,48 @@ public void SvgRenderer_Render_BoxWithCompartment_ProducesLineAndText()
         Assert.Contains("+ radius : Real", svgText, StringComparison.Ordinal);
     }
 
+    /// <summary>
+    ///     Render a LayoutBox with a Note shape, a compartment, and no Label/Keyword does not emit a
+    ///     divider line before the first compartment, since with no title area the divider would sit
+    ///     on the box's own top edge and (unlike a plain rectangle) protrude past the Note shape's
+    ///     folded-corner cutout as a stray line.
+    /// </summary>
+    [Fact]
+    public void SvgRenderer_Render_NoteBoxWithCompartmentAndNoTitle_OmitsLeadingDivider()
+    {
+        // Arrange: a Note-shaped box with a compartment but no Label/Keyword
+        var renderer = new SvgRenderer();
+        var compartment = new LayoutCompartment(null, ["Some body text"]);
+        var box = new LayoutBox(10, 10, 150, 80, null, 0, BoxShape.Note, [compartment], []);
+        var layout = new LayoutTree(200, 120, [box]);
+        var options = new RenderOptions(Themes.Light);
+        using var output = new MemoryStream();
+
+        // Act
+        renderer.Render(layout, options, output);
+
+        // Assert: no full-width divider <line> element is drawn at the box's own top edge (the
+        // previously buggy behavior), but the compartment row text still renders. Parsing as XML
+        // and inspecting the element's attributes (rather than matching a literal substring) keeps
+        // this robust to harmless formatting/attribute-ordering changes in the SVG serialization.
+        output.Position = 0;
+        var svgText = ReadAllText(output);
+        var document = System.Xml.Linq.XDocument.Parse(svgText);
+        var hasStrayDivider = document.Descendants()
+            .Where(e => e.Name.LocalName == "line")
+            .Any(e =>
+                IsClose(e.Attribute("x1")!.Value, 10.0) &&
+                IsClose(e.Attribute("y1")!.Value, 10.0) &&
+                IsClose(e.Attribute("x2")!.Value, 160.0) &&
+                IsClose(e.Attribute("y2")!.Value, 10.0));
+        Assert.False(hasStrayDivider);
+        Assert.Contains("Some body text", svgText, StringComparison.Ordinal);
+    }
+
+    /// <summary>Parses an SVG numeric attribute value and compares it to an expected value within a small tolerance.</summary>
+    private static bool IsClose(string attributeValue, double expected) =>
+        Math.Abs(double.Parse(attributeValue, System.Globalization.CultureInfo.InvariantCulture) - expected) < 0.01;
+
     /// <summary>
     ///     Render a LayoutBox with RoundedRectangle shape produces SVG output containing an
     ///     rx attribute, confirming that rounded corners are applied via the rx/ry attributes.