Trim cross corner sidewalk tip and fix outer arc skirt

Drop the sidewalk fan to (±jr,±jr) that made a sharp property-corner
spike, and emit a walk-height sidewalk vertical on the outer gray arc
so the skirt faces render instead of showing through.

Co-authored-by: 西风逍遥游 <sunxfancy@gmail.com>

src/modules/procgen/road/RoadBake.cpp

@@ -574,24 +574,24 @@ Result<void> bakeJunction(MeshBuild& mesh, const RoadNetwork& network, const Roa
                     const V3    b1 = arcPt(r1, t1);
                     const V3    c0 = arcPt(r2, t0);
                     const V3    c1 = arcPt(r2, t1);
-                    // Toward the outer corner center (sidewalk side).
+                    // Toward the outer corner center (property side) / toward asphalt.
                     const V3 inToCorner = normalize(V3{cx - a0.x, 0.f, cz - a0.z});
                     const V3 outToRoad  = inToCorner * -1.f;
 
-                    // Tops: asphalt-face → curb → sidewalk → corner disk, all +Y.
+                    // Tops: asphalt-face → curb → sidewalk ring. No fan to (jr,jr) —
+                    // that disk tip is the sharp property-corner spike.
                     appendOrientedQuad(mesh, V3{a0.x, curbTop, a0.z}, V3{b0.x, curbTop, b0.z},
                                        V3{b1.x, curbTop, b1.z}, V3{a1.x, curbTop, a1.z}, upN, 0.f, 1.f, 0.f, 1.f,
                                        RoadMaterial::Curb);
                     appendOrientedQuad(mesh, V3{b0.x, walkY, b0.z}, V3{c0.x, walkY, c0.z}, V3{c1.x, walkY, c1.z},
                                        V3{b1.x, walkY, b1.z}, upN, 0.f, 1.f, 0.f, 1.f, RoadMaterial::Sidewalk);
-                    appendOrientedTri(mesh, V3{cx, walkY, cz}, V3{c0.x, walkY, c0.z}, V3{c1.x, walkY, c1.z}, upN,
-                                      RoadMaterial::Sidewalk);
 
-                    // Vertical curb face toward asphalt / toward corner.
+                    // Vertical curb toward asphalt; sidewalk skirt on the outer gray arc.
                     appendOrientedQuad(mesh, V3{a0.x, y, a0.z}, V3{a1.x, y, a1.z}, V3{a1.x, curbTop, a1.z},
                                        V3{a0.x, curbTop, a0.z}, outToRoad, 0.f, 1.f, 0.f, 1.f, RoadMaterial::Curb);
-                    appendOrientedQuad(mesh, V3{c0.x, y, c0.z}, V3{c1.x, y, c1.z}, V3{c1.x, curbTop, c1.z},
-                                       V3{c0.x, curbTop, c0.z}, inToCorner, 0.f, 1.f, 0.f, 1.f, RoadMaterial::Curb);
+                    appendOrientedQuad(mesh, V3{c0.x, y, c0.z}, V3{c1.x, y, c1.z}, V3{c1.x, walkY, c1.z},
+                                       V3{c0.x, walkY, c0.z}, inToCorner, 0.f, 1.f, 0.f, 1.f,
+                                       RoadMaterial::Sidewalk);
                 }
             }
         }

test/procgen_road.cpp

@@ -327,9 +327,11 @@ TEST_CASE("procgen.road.scenes.crossJunctionCornerSidewalks") {
     CHECK_GE(sidewalkGroup, 0);
     auto sw = baked.value().mesh.copyGroup(sidewalkGroup);
     REQUIRE(sw);
-    // Outward-center curb returns: sidewalks sit near (jr,jr) inside the corner disk.
+    // Outward-center curb returns: sidewalk ring around (jr,jr), no tip disk to the center.
     const float jr = hubJr;
     int         arcHits = 0;
+    int         tipHits = 0;
+    int         outerSkirtHits = 0;
     for (int i = 0; i < sw->getVertexCount(); ++i) {
         const float x  = std::fabs(sw->getPositionX(i));
         const float z  = std::fabs(sw->getPositionZ(i));
@@ -337,10 +339,17 @@ TEST_CASE("procgen.road.scenes.crossJunctionCornerSidewalks") {
         const float dz = jr - z;
         if (dx < 0.05f || dz < 0.05f) continue;
         const float r = std::sqrt(dx * dx + dz * dz);
-        // Between sidewalk outer and curb face radii from the outer corner center.
+        // Sidewalk annulus between outer skirt and curb (no fan into r≈0 tip).
         if (r > 0.9f && r < 2.9f) ++arcHits;
+        if (r < 0.55f) ++tipHits;
+        const float nx = sw->getNormalX(i);
+        const float nz = sw->getNormalZ(i);
+        // Outer skirt faces toward the property corner (±jr,±jr).
+        if (r > 0.7f && r < 1.4f && (nx * dx + nz * dz) > 0.3f) ++outerSkirtHits;
     }
     CHECK_GT(arcHits, 16);
+    CHECK_EQ(tipHits, 0);
+    CHECK_GT(outerSkirtHits, 8);
 
     // Top faces must carry +Y normals (mesh3D CCW / lighting); flipped windings show dark.
     int upHits = 0, downHits = 0;