Fillets and chamfers ending on a boss's pieced wall or beside it, on a face that runs along its seam twice, and loops the loop blend refuses (#926)

Fillets and chamfers ending on a boss's pieced wall or beside it, on a face that runs along its seam twice, and loops the loop blend refuses

- A straight edge whose end meets one curved surface in several faces (a cylinder a join left
  in pieces) ends on that surface: the section is cut where it crosses each seam, which is
  shortened there; where no seam is crossed (the wall missing inside the other body) the
  section lies on the bared surface and the rest of the side edge becomes a seam.
- Two end faces that aren't both planes meeting in lines: each face takes the section's points
  on it, cut where it crosses the edge between them. Not where an end face runs on smoothly
  from a side (an earlier round): the corner build takes those.
- Face boundaries close over several connector edges.
- A face on a periodic surface running along its seam twice (as a STEP file gives it) is
  rebuilt the same way (#691).
- A curved chain ending square on a face that runs on past its side extends that face's seam.
- A smooth chain stops before an edge between faces that meet smoothly.
- A loop the loop blend refuses for its shape is blended edge by edge; refusals about its size
  stand.
- Action matrix: ACTION_MATRIX_ACTIONS and ACTION_MATRIX_VALIDITY for quick local runs; the
  fillets and chamfers that pass now recorded.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/kernel/src/curveblend.rs

@@ -1187,15 +1187,16 @@ fn curve_blend_with_limit(solid: &Solid, ids: &[mt::EdgeID], size: f64, r: f64,
             if consumed.contains_key(&id) {
                 continue;
             }
-            // At a slanted end the blend may stop past the seam's old end: the seam then runs
-            // on along its line or circle, within its planar face.
+            // At an end of an open chain the blend may stop past the seam's old end (a slanted end
+            // face, or one turning back past the side, as a box side beside a boss joined to it):
+            // the seam then runs on along its line or circle, within its planar face.
             let one_end = match (&a, &b) {
                 (Some(nv), None) => Some((seam.front().clone(), nv.clone())),
                 (None, Some(nv)) => Some((seam.back().clone(), nv.clone())),
                 _ => None,
             };
             if let Some((old, nv)) = one_end
-                && slanted.iter().any(|(k, ..)| verts.get(*k) == Some(&old))
+                && end_faces.iter().any(|(k, _)| verts.get(*k) == Some(&old))
             {
                 let on_tol = (size * 1e-5).max(1e-6);
                 let q = from_p3(nv.point());