fix(core): smooth tunnel entrance floor; verifier keeps baselines out of /tmp (L47); research R14

The demo tunnel's hard floor cap used a vertical Z - floorZ on a sloped Bezier floor, which is not a signed
distance, so marching cubes produced a staircase through the first 7 m (40-51 mm ripple, 82 mm steps). The
cap now uses the grade-normalised signed distance with a floor-adjacent bore re-application fading over the
entrance; mesh tile Z bounds include cavern bounds. New three-rail entrance audit: L46 fails, L47 passes.
verify: the cost baseline exports only build inputs into Saved/Linux/<out>/baseline-<commit> and removes it;
/tmp unchanged after a full tier. Demo off: owner hashes identical to L46. fast/medium/full PASS.
Known: sawtooth at the tunnel wall foot (next round). Research R14: Windows/MSVC readiness review.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Standalone/Core/src/ShapeWorldInternal.h

@@ -5973,6 +5973,10 @@ private:
             }
             const float centerX=bezier(t,0),centerY=bezier(t,1);
             const float floorZ=bezier(t,2);
+            const float floorHorizontalSpeed=std::hypot(derivative(t,0),derivative(t,1));
+            const float floorGrade=floorHorizontalSpeed>1.0e-5f
+                ?derivative(t,2)/floorHorizontalSpeed:0.0f;
+            const float floorDistanceScale=1.0f/std::sqrt(1.0f+floorGrade*floorGrade);
             const float radial=std::hypot(X-centerX,Y-centerY);
             const float radius=feature.boreRadiusVoxels;
             const float vertical=(Z-floorZ)/feature.boreHeightVoxels;
@@ -6000,11 +6004,12 @@ private:
                 return;
             }
             composed=SmoothMaxDistance(composed,-distance,feature.smoothWidthVoxels);
-            // The hard profile cap is deliberately applied after the smooth union and
-            // relief. Below it, native rock remains untouched; the narrow support above
-            // fills only baseline air.
+            // Apply a signed distance to the sloped floor plane. The old vertical
+            // height field made Marching Cubes quantize the shallow ramp into terraces.
+            // Below it, native rock remains untouched; the narrow support above fills
+            // only baseline air.
             if(radial<=radius)
-                composed=std::min(composed,Z-floorZ);
+                composed=std::min(composed,(Z-floorZ)*floorDistanceScale);
         };
         if(scoped)
             for(const auto index:tileQueries->cavernFeatureCandidates())apply(index);
@@ -6097,12 +6102,17 @@ private:
                 t=std::clamp(t-(dx*vx+dy*vy)/denominator,0.0f,1.0f);
             }
             const float floorZ=bezier(t,2);
+            const float floorHorizontalSpeed=std::hypot(derivative(t,0),derivative(t,1));
+            const float floorGrade=floorHorizontalSpeed>1.0e-5f
+                ?derivative(t,2)/floorHorizontalSpeed:0.0f;
+            const float floorDistanceScale=1.0f/std::sqrt(1.0f+floorGrade*floorGrade);
             const float radial=std::hypot(X-bezier(t,0),Y-bezier(t,1));
-            if(Z<floorZ)
+            const float floorDistance=(Z-floorZ)*floorDistanceScale;
+            const float floorSdfBand=std::max(1.0f,feature.floorSupportDepthVoxels);
+            if(Z<floorZ-floorSdfBand)
             {
-                // Re-evaluate the narrow fallback after passages and stamps, since
-                // those later operations may open air beneath an otherwise native
-                // floor. Negative native density is preserved by the min operation.
+                // Preserve the existing narrow support outside the signed-distance
+                // band beneath the floor.
                 if(capped>0.0f&&feature.floorSupportDepthVoxels>0.0f
                     &&Z>=floorZ-feature.floorSupportDepthVoxels
                     &&radial<feature.boreRadiusVoxels-0.12f)
@@ -6114,8 +6124,36 @@ private:
                 }
                 return;
             }
+            if(radial<=feature.boreRadiusVoxels&&Z<=floorZ+0.8f)
+            {
+                const float vertical=(Z-floorZ)/feature.boreHeightVoxels;
+                const float normalized=std::sqrt((radial/feature.boreRadiusVoxels)
+                    *(radial/feature.boreRadiusVoxels)+vertical*vertical);
+                float tunnelDistance=(normalized-1.0f)*std::min(
+                    feature.boreRadiusVoxels,feature.boreHeightVoxels);
+                if(feature.irregularityAmplitudeVoxels>0.0f)
+                {
+                    const float fade=SmoothUnit((Z-floorZ)/0.8f);
+                    tunnelDistance+=StampValueNoise(
+                        X-feature.controlPointsVoxels[0][0],
+                        Y-feature.controlPointsVoxels[0][1],Z-floorZ,
+                        feature.irregularityWavelengthVoxels,feature.irregularitySeed)
+                            *feature.irregularityAmplitudeVoxels*fade;
+                }
+                // Reapply the tunnel SDF in the floor-adjacent strip. Keep a narrow
+                // correction along the ramp, with a wider fade only at the stamped mouth.
+                const float heightAboveFloor=Z-floorZ;
+                const float mouthFade=1.0f-SmoothUnit(t/0.10f);
+                const float recarveWeight=heightAboveFloor<=0.25f?1.0f:mouthFade;
+                if(recarveWeight>0.0f)
+                {
+                    const float recarved=SmoothMaxDistance(capped,-tunnelDistance,
+                        feature.smoothWidthVoxels);
+                    capped=std::lerp(capped,recarved,recarveWeight);
+                }
+            }
             if(radial<=feature.boreRadiusVoxels)
-                capped=std::min(capped,Z-floorZ);
+                capped=std::min(capped,floorDistance);
         };
         if(scoped)
             for(const auto index:tileQueries->cavernFeatureCandidates())apply(index);