test(style): native-curve clip coverage — cubic segment + inline visual

Adds a CubicTo clip test (curve survives to the clip payload, not flattened)
and a self-contained ShapeClipPathVisualTest that samples the rendered pixels
(triangle clip ~50% coverage, base-at-bottom) to guard a dropped/empty clip,
wrong scale, or y-flip without a committed pixel baseline.

Author: DemchaAV

src/test/java/com/demcha/compose/document/dsl/ShapeContainerBuilderTest.java

@@ -198,6 +198,45 @@ void pathOutlineReachesTheClipPayloadAndRenders() throws Exception {
         }
     }
 
+    @Test
+    void cubicCurveOutlineKeepsItsCurveSegmentThroughTheClipPipeline() throws Exception {
+        // Every other path-clip test is line-only. A native cubic Bézier
+        // (curveTo) must survive to the clip payload as a CubicTo segment —
+        // NOT flattened to lines — and render without error, since native
+        // curves are the whole point of ShapeOutline.Path. This asserts the
+        // clip *payload*; ShapeClipPathVisualTest covers the rendered pixels.
+        try (DocumentSession session = GraphCompose.document()
+                .pageSize(200, 160)
+                .margin(DocumentInsets.of(16))
+                .create()) {
+
+            session.add(new ShapeContainerBuilder()
+                    .name("Petal")
+                    .path(120.0, 90.0, java.util.List.of(
+                            com.demcha.compose.document.style.DocumentPathSegment.moveTo(0.5, 1.0),
+                            com.demcha.compose.document.style.DocumentPathSegment.cubicTo(
+                                    1.1, 0.9, 1.0, 0.1, 0.5, 0.0),
+                            com.demcha.compose.document.style.DocumentPathSegment.cubicTo(
+                                    0.0, 0.1, -0.1, 0.9, 0.5, 1.0),
+                            com.demcha.compose.document.style.DocumentPathSegment.close()))
+                    .fillColor(BRAND)
+                    .center(spacer("Inside", 40.0, 16.0))
+                    .build());
+
+            List<PlacedFragment> fragments = session.layoutGraph().fragments();
+            int begin = indexOfPayload(fragments, ShapeClipBeginPayload.class);
+            assertThat(begin).isGreaterThanOrEqualTo(0);
+            ShapeOutline outline = ((ShapeClipBeginPayload) fragments.get(begin).payload()).outline();
+            assertThat(outline).isInstanceOf(ShapeOutline.Path.class);
+            assertThat(((ShapeOutline.Path) outline).segments())
+                    .as("the cubic segment must reach the clip payload, not be flattened to lines")
+                    .anyMatch(s -> s instanceof com.demcha.compose.document.style.DocumentPathSegment.CubicTo);
+
+            byte[] pdf = session.toPdfBytes();
+            assertThat(new String(pdf, 0, 5, java.nio.charset.StandardCharsets.US_ASCII)).isEqualTo("%PDF-");
+        }
+    }
+
     @Test
     void svgPathBridgeProducesAPathOutline() {
         // path(w, h, SvgPath) clips a container to an imported icon silhouette.

src/test/java/com/demcha/testing/visual/ShapeClipPathVisualTest.java

@@ -0,0 +1,98 @@
+package com.demcha.testing.visual;
+
+import com.demcha.compose.GraphCompose;
+import com.demcha.compose.document.api.DocumentSession;
+import com.demcha.compose.document.dsl.ShapeBuilder;
+import com.demcha.compose.document.dsl.ShapeContainerBuilder;
+import com.demcha.compose.document.style.ClipPolicy;
+import com.demcha.compose.document.style.DocumentColor;
+import com.demcha.compose.document.style.DocumentInsets;
+import com.demcha.compose.document.style.DocumentPathSegment;
+import com.demcha.compose.testing.visual.PdfVisualRegression;
+import org.junit.jupiter.api.Test;
+
+import java.awt.image.BufferedImage;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Deterministic visual check that a {@code ShapeOutline.Path} clip actually
+ * shapes the rendered pixels — the gap the {@code %PDF-} smoke tests cannot
+ * cover. A full-box red layer clipped to an upward triangle must paint roughly
+ * half the box (a triangle is half its bounding box) with the wide base at the
+ * BOTTOM. So a dropped clip (≈100% red), an empty clip (≈0% red), a wrong scale,
+ * and a y-flip (apex/base swapped) all fail this test.
+ *
+ * <p>Self-contained on purpose: it samples the in-memory render instead of
+ * diffing a committed PNG baseline, so it stays deterministic and
+ * anti-aliasing-tolerant across platforms without a blessed pixel reference.</p>
+ */
+class ShapeClipPathVisualTest {
+
+    private static final int BOX = 120;
+
+    @Test
+    void pathClipShapesTheRenderedPixelsRightSideUp() throws Exception {
+        BufferedImage page = PdfVisualRegression.standard()
+                .renderPages(renderTriangleClip())
+                .get(0);
+
+        int w = page.getWidth();
+        int h = page.getHeight();
+        long red = 0;
+        long redTop = 0;
+        long redBottom = 0;
+        for (int y = 0; y < h; y++) {
+            for (int x = 0; x < w; x++) {
+                if (isRed(page.getRGB(x, y))) {
+                    red++;
+                    if (y < h / 2) {
+                        redTop++;
+                    } else {
+                        redBottom++;
+                    }
+                }
+            }
+        }
+
+        double fraction = (double) red / ((long) w * h);
+        assertThat(fraction)
+                .as("clipped red triangle should cover ~half the box "
+                        + "(clip applied, right scale) — got %.3f", fraction)
+                .isBetween(0.30, 0.70);
+        assertThat(redBottom)
+                .as("wide base at the bottom, narrow apex at the top — guards a y-flip")
+                .isGreaterThan(redTop * 2);
+    }
+
+    /** A 120x120 container clipping a full-box red layer to an upward triangle. */
+    private static byte[] renderTriangleClip() throws Exception {
+        try (DocumentSession session = GraphCompose.document()
+                .pageSize(BOX, BOX)
+                .margin(DocumentInsets.zero())
+                .create()) {
+            session.add(new ShapeContainerBuilder()
+                    .name("TriangleClip")
+                    .path(BOX, BOX, List.of(
+                            DocumentPathSegment.moveTo(0.5, 1.0),   // apex, top (y grows up)
+                            DocumentPathSegment.lineTo(1.0, 0.0),   // base, bottom-right
+                            DocumentPathSegment.lineTo(0.0, 0.0),   // base, bottom-left
+                            DocumentPathSegment.close()))
+                    .clipPolicy(ClipPolicy.CLIP_PATH)
+                    .layer(new ShapeBuilder()
+                            .size(BOX, BOX)
+                            .fillColor(DocumentColor.rgb(220, 20, 20))
+                            .build())
+                    .build());
+            return session.toPdfBytes();
+        }
+    }
+
+    private static boolean isRed(int rgb) {
+        int r = (rgb >> 16) & 0xFF;
+        int g = (rgb >> 8) & 0xFF;
+        int b = rgb & 0xFF;
+        return r > 140 && g < 110 && b < 110;
+    }
+}