feat: preserve body history and placed modelling workflows

Record ownership transfers in the timeline so earlier Join/Cut membership,
world placement, machining data and styles survive component moves, edits,
independent copying, undo and reopening. Preserve pending positions in history
snapshots and keep constructor transfers ordered during feature redefinition.

Retain shallow sheet pockets and exact planar intersection islands through
unfold/refold, with depth-aware flat previews and DXF export. Store explicit
3D wire coordinate spaces and migrate known legacy provenance without moving
saved points or analytic fits.

Infer unique eligible cylindrical Emboss targets, align Revolve manipulators
with actual extent geometry, and discard obsolete preview errors after input
correction. Certify constructed and immutable imported face styles using exact
source metadata while preserving legacy face names. Upgrade designs to format10
with bounded validation and geometry-preserving legacy migration.

crates/kernel/src/step_in/mod.rs

@@ -34,6 +34,10 @@ const MAX_VISITS: usize = 100_000;
 /// A body read from a STEP file.
 #[derive(Clone, Debug)]
 pub struct ImportedBody {
+    /// Immutable STEP source item, scoped to its embedded payload.
+    pub source_item: u64,
+    /// Original STEP face entity of each kernel face, including seam pieces.
+    pub face_origin: Vec<u64>,
     /// Solid name (the brep's label), else the product name.
     pub name: String,
     pub body: Body,
@@ -510,7 +514,21 @@ impl<'a> Reader<'a> {
                                 .collect();
                             let paint = crate::Paint { opacity: self.opacity.get(&item).copied().unwrap_or(1.0), faces };
                             let body = body.with_color(color).with_paint(Some(paint));
-                            self.bodies.push(ImportedBody { name, body, color, path: path.to_vec(), closed, file_faces });
+                            let identities = face_origin
+                                .iter()
+                                .map(|face| Some(crate::FaceSource::Imported { item, face: *face, payload_sha256: None, producer: None }))
+                                .collect();
+                            let body = body.with_face_sources(Some(std::sync::Arc::new(identities)));
+                            self.bodies.push(ImportedBody {
+                                name,
+                                body,
+                                color,
+                                path: path.to_vec(),
+                                closed,
+                                file_faces,
+                                source_item: item,
+                                face_origin,
+                            });
                         }
                         Err(err) => {
                             let label = self.label(item);