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/engine/src/tests.rs

@@ -864,7 +864,14 @@ fn holes_at_sketch_points_threads_and_components() {
     let text = s.doc.to_json();
     let back = solvecraft_doc::Document::from_json(&text).unwrap();
     assert_eq!(back.components.len(), 2);
-    assert_eq!(back.body_components.len(), 1);
+    let assigned = r["components"][0]["component"].as_u64().unwrap();
+    let transfer = r["components"][0]["feature"].as_u64().unwrap();
+    assert!(
+        matches!(&back.feature(transfer).unwrap().kind, solvecraft_doc::FeatureKind::BodyTransfer { bodies, to, .. } if bodies == &["Shaft"] && *to == assigned)
+    );
+    let reopened = Session::new(back);
+    assert_eq!(reopened.model.state().body("Shaft").unwrap().component, assigned);
+    assert_eq!(reopened.world_state().threads.len(), s.world_state().threads.len());
 }
 
 #[test]
@@ -985,11 +992,22 @@ fn components_occurrences_and_world_placement() {
     run(&mut s, "component.capture_position", json!({}));
     assert!(s.pending_moves.is_empty());
     assert!((bbox(&mut s, "ArmBody")["min"][2].as_f64().unwrap() - 5.0).abs() < 1e-9);
-    // Bodies and sketches move between components.
-    run(&mut s, "component.move_bodies", json!({"bodies": ["Base"], "component": "Arm"}));
+    // A definition placed twice cannot receive one world body without duplicating it.
+    let document = s.doc.to_json();
+    let pending = s.pending_moves.clone();
+    let error = s.execute("component.move_bodies", &json!({"bodies": ["Base"], "component": "Arm"})).unwrap_err();
+    assert!(error.to_string().contains("one source and destination placement"), "{error}");
+    assert_eq!(s.doc.to_json(), document);
+    assert_eq!(s.pending_moves, pending);
+    // The independent Paste New result has one placement and can receive it.
+    let copied = pn["component"].as_u64().unwrap();
+    run(&mut s, "component.move_bodies", json!({"bodies": ["Base"], "component": copied}));
     let l = run(&mut s, "component.list", json!({}));
     let arm = l["components"].as_array().unwrap().iter().find(|x| x["id"] == cid).unwrap().clone();
-    assert!(arm["bodies"].as_array().unwrap().iter().any(|b| b == "Base"), "{arm}");
+    assert!(!arm["bodies"].as_array().unwrap().iter().any(|b| b == "Base"), "{arm}");
+    let receiver = l["components"].as_array().unwrap().iter().find(|x| x["id"] == copied).unwrap();
+    assert!(receiver["bodies"].as_array().unwrap().iter().any(|b| b == "Base"), "{receiver}");
+    assert_eq!(bbox(&mut s, "Base")["min"], json!([0.0, 0.0, 0.0]));
     run(&mut s, "sketch.create", json!({"plane": "XY", "name": "S1"}));
     run(&mut s, "sketch.finish", json!({}));
     run(&mut s, "component.move_sketches", json!({"sketches": ["S1"], "component": cid}));
@@ -999,8 +1017,9 @@ fn components_occurrences_and_world_placement() {
     assert_eq!(s.doc.find_feature("S1").unwrap().component, 0);
     run(&mut s, "edit.redo", json!({}));
     run(&mut s, "timeline.roll_to", json!({"position": 1}));
-    // Only Base is left; it now lives in Arm, which is placed twice (original and instance).
-    assert_eq!(s.world_state().bodies.len(), 2);
+    // The ownership boundary is later: before it Base remains the sole root body.
+    assert_eq!(s.world_state().bodies.len(), 1);
+    assert_eq!(s.world_state().body("Base").unwrap().component, 0);
     run(&mut s, "timeline.roll_to", json!({}));
     // Saved and loaded; older designs get occurrences.
     let back = solvecraft_doc::Document::from_json(&s.doc.to_json()).unwrap();