M1: robust revolves touching the axis (cone shells), partial revolves toward the sketch normal, coplanar profile growth for joins/cuts, membership-checked booleans, per-face measurement fallback

Oracle: 18/29 parts match Fusion.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/kernel/src/measure.rs

@@ -1,5 +1,5 @@
 use serde::Serialize;
-use solvecraft_geom::{Aabb3, Vec3};
+use solvecraft_geom::{Aabb3, Mesh, Vec3};
 
 use crate::Result;
 use crate::body::Body;
@@ -22,21 +22,46 @@ pub struct BodyMeasure {
     pub merged: TopoCounts,
 }
 
-/// Measure a body from a fine tessellation (chord tolerance 5e-5 of the body size). Curved
-/// faces are slightly under-estimated (relative error typically below 2e-4).
+/// Per-face sums: area, 6 × signed volume and 24 × first moments (divergence theorem, origin 0).
+fn face_sums(m: &Mesh, nf: usize) -> Vec<(f64, f64, Vec3)> {
+    let mut out = vec![(0.0, 0.0, Vec3::ZERO); nf];
+    for (t, f) in m.triangles.iter().zip(&m.tri_face) {
+        let (Some([a, b, c]), Some(slot)) = (m.tri(t), out.get_mut(*f as usize)) else { continue };
+        let d = a.dot(b.cross(c));
+        slot.0 += (b - a).cross(c - a).len() * 0.5;
+        slot.1 += d;
+        slot.2 += (a + b + c) * d;
+    }
+    out
+}
+
+/// Measure a body from a fine tessellation (chord tolerance 5e-5 of the body size). Faces whose
+/// fine tessellation disagrees with a coarse one (a meshing failure) use the coarse result.
 pub fn measure(b: &Body) -> Result<BodyMeasure> {
     let size = b.size();
-    let m2 = b.tessellate((size * 5e-5).max(1e-4))?;
-    let a2 = m2.measure();
+    let fine = b.tessellate((size * 5e-5).max(1e-4))?;
+    let coarse = b.tessellate((size * 1e-3).max(1e-3))?;
+    let nf = b.face_count();
+    let (sf, sc) = (face_sums(&fine, nf), face_sums(&coarse, nf));
+    let (mut area, mut v6, mut mom) = (0.0, 0.0, Vec3::ZERO);
+    for (f, c) in sf.iter().zip(&sc) {
+        let bad = (f.0 - c.0).abs() > 0.01 * c.0.max(f.0) + 1e-9;
+        let pick = if bad { c } else { f };
+        area += pick.0;
+        v6 += pick.1;
+        mom += pick.2;
+    }
+    let volume = v6 / 6.0;
+    let centroid = if v6.abs() > 1e-12 { mom / (4.0 * v6) } else { fine.bounds().center() };
     Ok(BodyMeasure {
-        volume: a2.volume,
-        area: a2.area,
-        centroid: a2.centroid,
-        bbox: m2.bounds(),
+        volume,
+        area,
+        centroid,
+        bbox: coarse.bounds().union(&fine.bounds()),
         faces: b.face_count(),
         edges: b.edge_count(),
         vertices: b.vertex_count(),
         shells: b.shell_count(),
-        merged: merged_topology(b, &m2)?,
+        merged: merged_topology(b, &coarse)?,
     })
 }