Components are frames (user bug #4)

What a component holds moves with its occurrence, and picks in the world land in the
component's frame:
- Sketches and construction planes show where their component is placed (free move, joint
  drive, Capture Position); sketch.inspect reports sketch points in the world.
- frames.rs maps a command's world picks into the frame of the body they lie on (through the
  inverse of its placement: a moved component or a pasted instance), points that make new
  geometry into the active component's frame, and directions with them; instance body names
  ("Body1 (Pin:2)") become the component's body. Fillet/chamfer edges, shell/offset/draft
  faces, face extrude/revolve, sketch on face, holes, sheet metal and plastic picks, primitives,
  appearance faces, analyses. Once per command (not again for commands run by commands); the
  active-frame fallback stays for commands without a table. Nothing changes while every
  placement is the identity.
- component.move_bodies keeps a body where it is in the world (Document.body_offsets: from the
  new component's frame to the one it was made in; renames and deleted components follow).
- The UI reads the placed model (Session::world_state) for display, picking, sketch editing and
  dialogs; live previews use it once anything is placed.
Tests (engine): sketches and construction planes move (and turn) with the component; world
picks fillet, sketch, hole and make boxes in a moved component; a pick on a pasted instance;
move_bodies keeps the world place there and back; a sketch on a face follows a Move feature.
QA's s34 now runs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/doc/src/eval.rs

@@ -2291,7 +2291,10 @@ pub fn world_state(doc: &Document, st: &ModelState) -> ModelState {
         let ident = crate::is_identity(&m);
         for b in st.bodies.iter().filter(|b| doc.body_component(&b.name, b.feature) == comp) {
             let name = if primary { b.name.clone() } else { format!("{} ({})", b.name, label()) };
-            let body = if ident { b.body.clone() } else { kernel::transform_matrix(&b.body, m).unwrap_or_else(|_| b.body.clone()) };
+            // A body moved in from another component keeps its place (its offset).
+            let bm = doc.body_offsets.get(&b.name).map(|o| crate::mat_mul(&m, o)).unwrap_or(m);
+            let body =
+                if crate::is_identity(&bm) { b.body.clone() } else { kernel::transform_matrix(&b.body, bm).unwrap_or_else(|_| b.body.clone()) };
             out.bodies.push(ModelBody::new(name, body, b.feature));
         }
         if primary {