Shell: its planar walls carry their shell roles again

The SMLib port of shell dropped with_shell_planar_sources (then deleted it as dead
code), so a shelled body's kept walls and their inner linings had no ShellPlanar
certificate: a sketch or press-pull on a shell's floor lost its attachment (the Pi
case's Sketch2 and everything after it, press_pull_on_the_pi_case_floor) and the
shell certificate tests found no inner/outer face. The roles come from the input's
exact planar supports, so they apply to SMLib's result unchanged.

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

crates/kernel/src/planar_sources.rs

@@ -141,6 +141,12 @@ impl Body {
         self.map_planar_sources(&[input], None, None, &[], false)
     }
 
+    /// Generate distinct outer/inner roles from the exact original supports of
+    /// an inside shell. Generated rims and curved walls are intentionally absent.
+    pub(crate) fn with_shell_planar_sources(self, input: &Body, thickness: f64, open: &[Vec3]) -> Result<Self> {
+        self.map_planar_sources(&[input], Some(thickness), None, open, false)
+    }
+
     /// Retain exact shell roles, and construction roles for Cut, only on unchanged
     /// supports without a competing coplanar tool. No imported or fitted role is inferred.
     pub(crate) fn with_preserved_boolean_planar_sources(self, input: &Body, tool: &Body, constructed: bool) -> Result<Self> {

crates/kernel/src/polyhedron.rs

@@ -185,10 +185,12 @@ fn polyhedron_record(hs: &[HalfSpace], verts: &[Vec3], faces: &[(usize, Vec<usiz
 }
 
 /// Hollow a body: walls of `thickness` inside, open at the faces under `open` (SMLib's shell).
-/// The result's history is over `[b]`: the inner walls are offsets of the faces they line.
+/// The result's history is over `[b]`: the inner walls are offsets of the faces they line. Each
+/// kept planar wall and its inner lining carry the outer and inner shell roles of the face they
+/// came from (face certificates: sketches and press-pulls attach to them).
 pub fn shell(b: &Body, open: &[Vec3], thickness: f64) -> Result<Body> {
     let _span = solidcraft_profile::span("kernel", "shell");
-    crate::offset_backend::shell(b, open, thickness)
+    crate::offset_backend::shell(b, open, thickness)?.with_shell_planar_sources(b, thickness, open)
 }
 
 /// Tilt the faces near `faces` by `angle` about their line on the neutral plane, so that they