fix: restore shell and cut wall topology in 0.2.1

crates/kernel/src/prism.rs

@@ -683,12 +683,17 @@ fn sew_stack(plane: &Plane, d: Vec3, pa: &Prism, pb: &Prism, tol: f64) -> Option
         };
         slabs.push(oriented(&s));
     }
-    sew_sections(plane, d, &levels, &slabs, tol)
+    sew_sections(plane, d, &levels, &slabs, tol, false)
 }
 
 /// Sew the exact sections between successive levels, including empty gaps.
-fn sew_sections(plane: &Plane, d: Vec3, levels: &[f64], slabs: &[Vec<Region2>], tol: f64) -> Option<Result<Body>> {
-    if levels.len() != slabs.len() + 1 || slabs.len() > 128 || plane.normal().dot(d) < 1. - 1e-12 {
+fn sew_sections(plane: &Plane, d: Vec3, levels: &[f64], slabs: &[Vec<Region2>], tol: f64, coalesce: bool) -> Option<Result<Body>> {
+    if levels.len() != slabs.len() + 1
+        || slabs.len() > 128
+        || plane.normal().dot(d) < 1. - 1e-12
+        || levels.iter().any(|z| !z.is_finite())
+        || levels.windows(2).any(|z| z[0] >= z[1])
+    {
         return None;
     }
     let mut blocks = Vec::new();
@@ -732,7 +737,7 @@ fn sew_sections(plane: &Plane, d: Vec3, levels: &[f64], slabs: &[Vec<Region2>],
                     pieces.push(piece);
                 }
             } else {
-                let piece = sew_connected_sections(plane, d, &levels[first..=end], &slabs[first..end], tol)
+                let piece = sew_connected_sections(plane, d, &levels[first..=end], &slabs[first..end], tol, coalesce)
                     .ok_or_else(|| KernelError::Failed("stepped prism construction failed".into()))??;
                 remaining_faces =
                     remaining_faces.checked_sub(piece.face_count()).ok_or_else(|| KernelError::Failed("prism output face budget".into()))?;
@@ -765,8 +770,18 @@ fn sew_sections(plane: &Plane, d: Vec3, levels: &[f64], slabs: &[Vec<Region2>],
     })())
 }
 
+/// Stable exact identity for the bounded analytic segment subset.
+fn wall_key(s: &Seg2) -> Option<[u64; 6]> {
+    let bits = |v: f64| v.is_finite().then(|| if v == 0. { 0 } else { v.to_bits() });
+    match s {
+        Seg2::Line { a, b } => Some([0, bits(a.x)?, bits(a.y)?, bits(b.x)?, bits(b.y)?, 0]),
+        Seg2::Arc { center, radius, start, sweep } => Some([1, bits(center.x)?, bits(center.y)?, bits(*radius)?, bits(*start)?, bits(*sweep)?]),
+        _ => None,
+    }
+}
+
 /// A genuinely stepped connected axial block has no single extrusion footprint.
-fn sew_connected_sections(plane: &Plane, d: Vec3, levels: &[f64], slabs: &[Vec<Region2>], tol: f64) -> Option<Result<Body>> {
+fn sew_connected_sections(plane: &Plane, d: Vec3, levels: &[f64], slabs: &[Vec<Region2>], tol: f64, coalesce: bool) -> Option<Result<Body>> {
     use crate::sew::{EdgeSpec, FaceSpec, SurfSpec};
     // Faces at each level: up where the slab below sticks out, down where the one above does.
     let diff = |x: &[Region2], y: &[Region2]| -> Option<Vec<Region2>> {
@@ -800,30 +815,61 @@ fn sew_connected_sections(plane: &Plane, d: Vec3, levels: &[f64], slabs: &[Vec<R
             _ => EdgeSpec::Line { a: at(sg.start(), z), b: at(sg.end(), z) },
         }
     };
-    let mut faces: Vec<FaceSpec> = Vec::new();
-    for (i, s) in slabs.iter().enumerate() {
-        let (z0, z1) = (*levels.get(i)?, *levels.get(i + 1)?);
-        for lp in loops_of(s) {
+    // Exact oriented generated segments alone define a run. No support fitting,
+    // proximity matching, or old face lineage is used here.
+    let mut runs: Vec<(usize, usize, Seg2)> = Vec::new();
+    let mut last = std::collections::BTreeMap::new();
+    let mut remaining = MAX_PLANAR_SEGMENTS * 2;
+    for (i, slab) in slabs.iter().enumerate() {
+        for lp in loops_of(slab) {
             for sg0 in &lp.segs {
                 for sg in split_seg(sg0, &pts, tol)? {
-                    let (a, b) = (sg.start(), sg.end());
-                    let lp3 = vec![
-                        edge(&sg, z0),
-                        EdgeSpec::Line { a: at(b, z0), b: at(b, z1) },
-                        edge(&sg.reversed(), z1),
-                        EdgeSpec::Line { a: at(a, z1), b: at(a, z0) },
-                    ];
-                    let tangent = plane.dir_to_world(sg.derivative(0.5));
-                    let outward = tangent.cross(d).normalized()?;
-                    let surface = match sg {
-                        Seg2::Arc { .. } => SurfSpec::Extruded { a: at(a, z0), b: at(b, z0), mid: at(sg.point_at(0.5), z0), dir: d * (z1 - z0) },
-                        _ => SurfSpec::Plane,
-                    };
-                    faces.push(FaceSpec { loops: vec![lp3], surface, probe: Some((at(sg.point_at(0.5), (z0 + z1) / 2.0), outward)) });
+                    remaining = remaining.checked_sub(1)?;
+                    let key = wall_key(&sg)?;
+                    if coalesce {
+                        if let Some(&index) = last.get(&key) {
+                            let run: &mut (usize, usize, Seg2) = runs.get_mut(index)?;
+                            if run.1 == i {
+                                run.1 = i + 1;
+                                continue;
+                            }
+                            // Duplicate oriented boundaries in one slab are not
+                            // a valid reason to reconstruct a larger wall.
+                            if run.1 == i + 1 {
+                                return None;
+                            }
+                        }
+                        last.insert(key, runs.len());
+                    }
+                    runs.push((i, i + 1, sg));
                 }
             }
         }
     }
+    let mut faces: Vec<FaceSpec> = Vec::new();
+    let mut sources = Vec::new();
+    for (first, end, sg) in runs {
+        let (z0, z1) = (levels[first], levels[end]);
+        let (a, b) = (sg.start(), sg.end());
+        let mut lp3 = Vec::with_capacity(2 + 2 * (end - first));
+        lp3.push(edge(&sg, z0));
+        // Keep station vertices at both ends: neighboring stepped walls/caps
+        // must share complete edges rather than create T-junctions.
+        for k in first..end {
+            lp3.push(EdgeSpec::Line { a: at(b, levels[k]), b: at(b, levels[k + 1]) });
+        }
+        lp3.push(edge(&sg.reversed(), z1));
+        for k in (first..end).rev() {
+            lp3.push(EdgeSpec::Line { a: at(a, levels[k + 1]), b: at(a, levels[k]) });
+        }
+        let outward = plane.dir_to_world(sg.derivative(0.5)).cross(d).normalized()?;
+        let surface = match sg {
+            Seg2::Arc { .. } => SurfSpec::Extruded { a: at(a, z0), b: at(b, z0), mid: at(sg.point_at(0.5), z0), dir: d * (z1 - z0) },
+            _ => SurfSpec::Plane,
+        };
+        faces.push(FaceSpec { loops: vec![lp3], surface, probe: Some((at(sg.point_at(0.5), (z0 + z1) / 2.0), outward)) });
+        sources.push((end > first + 1).then_some(crate::FaceSource::ExtrudeSide { segment: sg, plane: None, coalesced: true }));
+    }
     for (z, up, rs) in &caps {
         for r in rs {
             let mut loops = Vec::new();
@@ -836,9 +882,10 @@ fn sew_connected_sections(plane: &Plane, d: Vec3, levels: &[f64], slabs: &[Vec<R
                 loops.push(segs.iter().map(|sg| edge(sg, *z)).collect::<Vec<_>>());
             }
             faces.push(FaceSpec { loops, surface: SurfSpec::Plane, probe: None });
+            sources.push(None);
         }
     }
-    Some(crate::sew::sew_touching(&faces))
+    Some(crate::sew::sew_touching_with_sources(&faces, &sources))
 }
 
 fn simple_prism_boolean(a: &Body, b: &Body, op: BoolOp) -> Option<Result<Option<Body>>> {
@@ -1055,7 +1102,19 @@ fn stack_boolean(a: &Body, b: &Body, op: BoolOp) -> Option<Result<Option<Body>>>
     if slabs.iter().all(Vec::is_empty) {
         return Some(Ok(None));
     }
-    sew_sections(&plane, d, &levels, &slabs, tol).map(|r| r.map(Some))
+    sew_sections(
+        &plane,
+        d,
+        &levels,
+        &slabs,
+        tol,
+        op == BoolOp::Cut
+            && a.split_keep().is_empty()
+            && b.split_keep().is_empty()
+            && a.paint().is_none_or(|p| p.faces.is_empty())
+            && b.paint().is_none_or(|p| p.faces.is_empty()),
+    )
+    .map(|r| r.map(Some))
 }
 
 pub(crate) fn prism_boolean(a: &Body, b: &Body, op: BoolOp) -> Option<Result<Option<Body>>> {
@@ -1144,7 +1203,12 @@ mod planar_tests {
                 assert!(mesh.contains(Vec3::new(21., 21., 3.)));
                 assert!(!mesh.contains(Vec3::new(25., 25., 3.)));
                 assert!(mesh.contains(Vec3::new(25., 25., 22.)));
-                assert!(lump.face_sources().is_none_or(|s| s.iter().all(Option::is_none)), "genuinely stepped geometry remains uncertified");
+                assert!(
+                    lump.face_sources().is_none_or(|s| s
+                        .iter()
+                        .all(|s| s.is_none() || matches!(s, Some(crate::FaceSource::ExtrudeSide { coalesced: true, plane: None, .. })))),
+                    "genuinely stepped geometry has no durable certificate"
+                );
                 assert!((mesh.measure().volume - (18. * (100. - 4. * std::f64::consts::PI) + 500.)).abs() < 0.02);
             }
         }
@@ -1152,6 +1216,72 @@ mod planar_tests {
         assert_eq!(crate::step_export(&[&tool], "tool").unwrap(), before_tool);
         assert_eq!(crate::step_export(&[&roof], "roof").unwrap(), before_roof);
     }
+    #[test]
+    fn contiguous_analytic_walls_remove_faces_but_retain_vertical_stations() {
+        for curved in [false, true] {
+            let outer = if curved {
+                Region2 { outer: Loop2::circle(Vec2::ZERO, 10.), holes: vec![] }
+            } else {
+                rectangle(Vec2::new(-10., -10.), Vec2::new(10., 10.))
+            };
+            let mut upper = outer.clone();
+            upper.holes.push(if curved {
+                Loop2::circle(Vec2::ZERO, 5.).reversed()
+            } else {
+                rectangle(Vec2::new(-5., -5.), Vec2::new(5., 5.)).outer.reversed()
+            });
+            let slabs = vec![vec![outer], vec![upper]];
+            let old = sew_sections(&Plane::XY, Vec3::Z, &[0., 2., 20.], &slabs, 1e-7, false).unwrap().unwrap();
+            let merged = sew_sections(&Plane::XY, Vec3::Z, &[0., 2., 20.], &slabs, 1e-7, true).unwrap().unwrap();
+            let count = if curved { 2 } else { 4 };
+            assert_eq!(old.face_count() - merged.face_count(), count);
+            let marked: Vec<_> = merged.solid.face_iter().enumerate().filter(|(i, _)| merged.face_was_coalesced(*i)).collect();
+            assert_eq!(marked.len(), count);
+            for (_, face) in marked {
+                assert_eq!(face.boundaries()[0].len(), 6, "all axial station vertices are retained");
+                let heights: Vec<_> = face.vertex_iter().map(|v| v.point().z).collect();
+                for z in [0., 2., 20.] {
+                    assert!(heights.contains(&z));
+                }
+            }
+            assert!(old.face_sources().is_none_or(|s| s.iter().all(Option::is_none)));
+            let expected = if curved { std::f64::consts::PI * (100. * 20. - 25. * 18.) } else { 400. * 20. - 100. * 18. };
+            let mesh = merged.tessellate(1e-5).unwrap();
+            assert!((mesh.measure().volume - expected).abs() < 0.03);
+            assert!(mesh.contains(Vec3::new(0., 0., 1.)));
+            assert!(!mesh.contains(Vec3::new(0., 0., 10.)));
+            assert!(merged.validity().is_empty());
+            assert_ne!(wall_key(&slabs[0][0].outer.segs[0]), wall_key(&slabs[0][0].outer.segs[0].reversed()));
+        }
+    }
+
+    #[test]
+    fn cut_run_coalescing_respects_authored_splits_and_face_paint() {
+        let region = Region2 { outer: Loop2::circle(Vec2::ZERO, 10.), holes: vec![] };
+        let tool_region = Region2 { outer: Loop2::circle(Vec2::ZERO, 5.), holes: vec![] };
+        let stock = crate::extrude(&Plane::XY, &[region], 0., 20.).unwrap().pop().unwrap();
+        let cutter = crate::extrude(&Plane::XY, &[tool_region], 2., 22.).unwrap().pop().unwrap();
+        let merged = stack_boolean(&stock, &cutter, BoolOp::Cut).unwrap().unwrap().unwrap();
+        let protected = [
+            stock.clone().with_split_lines(Some(std::sync::Arc::new(vec![vec![Vec3::new(10., 0., 0.), Vec3::new(10., 0., 20.)]]))),
+            stock.with_paint(Some(crate::Paint { opacity: 1., faces: vec![crate::FacePaint { face: 0, color: [1., 0., 0.], opacity: 1. }] })),
+        ];
+        for input in protected {
+            let output = stack_boolean(&input, &cutter, BoolOp::Cut).unwrap().unwrap().unwrap();
+            assert_eq!(output.face_count(), merged.face_count() + 2);
+            assert!((0..output.face_count()).all(|i| !output.face_was_coalesced(i)));
+            // Independent circular chord-volume bound: 2*pi*(10*20+5*18)*1e-5 < .019.
+            let expected = std::f64::consts::PI * (100. * 20. - 25. * 18.);
+            for body in [&output, &merged] {
+                let mesh = body.tessellate(1e-5).unwrap();
+                assert!((mesh.measure().volume - expected).abs() < 0.03);
+                assert!(mesh.contains(Vec3::new(0., 0., 1.)));
+                assert!(!mesh.contains(Vec3::new(0., 0., 10.)));
+                assert!(mesh.contains(Vec3::new(7., 0., 10.)));
+            }
+        }
+    }
+
     #[test]
     fn annular_inward_tool_recovers_exact_stacks_before_cap_policy() {
         let plane = Plane::XY;