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/assembly.rs

@@ -298,6 +298,43 @@ impl Document {
         out
     }
 
+    /// Every body as the world shows it: its world name ("Body1", or "Body1 (Occ:2)" for a
+    /// further instance), its component, the occurrence path, and the transform from the frame
+    /// its geometry is in to the world.
+    pub fn body_frames(&self, st: &crate::ModelState) -> Vec<(String, u64, Vec<u64>, Mat)> {
+        let mut out = Vec::new();
+        for (comp, path, m) in self.placements() {
+            let primary = path == self.first_path(comp);
+            let label = || -> String {
+                path.iter().filter_map(|id| self.occurrences.iter().find(|o| o.id == *id)).map(|o| o.name.as_str()).collect::<Vec<_>>().join("/")
+            };
+            for b in st.bodies.iter().filter(|b| self.body_component(&b.name, b.feature) == comp) {
+                let name = if primary { b.name.clone() } else { format!("{} ({})", b.name, label()) };
+                let w = match self.body_offsets.get(&b.name) {
+                    Some(o) => mat_mul(&m, o),
+                    None => m,
+                };
+                out.push((name, comp, path.clone(), w));
+            }
+        }
+        out
+    }
+
+    /// The occurrence path of a component's first placement.
+    pub fn first_path(&self, component: u64) -> Vec<u64> {
+        let mut path = Vec::new();
+        let mut c = component;
+        for _ in 0..1000 {
+            if c == 0 {
+                break;
+            }
+            let Some(o) = self.occurrence_of(c) else { break };
+            path.insert(0, o.id);
+            c = o.parent;
+        }
+        path
+    }
+
     /// Is `a` inside `b` (or `b` itself)?
     pub fn component_within(&self, a: u64, b: u64) -> bool {
         let mut c = a;

crates/doc/src/document.rs

@@ -1128,6 +1128,10 @@ pub struct Document {
     /// Bodies moved into another component than their feature's (by body name).
     #[serde(default, skip_serializing_if = "std::collections::BTreeMap::is_empty")]
     pub body_components: std::collections::BTreeMap<String, u64>,
+    /// Bodies moved into another component keep their place in the world: the transform from
+    /// the new component's frame to the frame the body was made in (by body name).
+    #[serde(default, skip_serializing_if = "std::collections::BTreeMap::is_empty")]
+    pub body_offsets: std::collections::BTreeMap<String, crate::Mat>,
     /// Browser groups (folders of bodies, sketches or construction planes).
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub browser_groups: Vec<BrowserGroup>,
@@ -1196,6 +1200,7 @@ impl Document {
             configs: Default::default(),
             parts: Default::default(),
             body_components: Default::default(),
+            body_offsets: Default::default(),
             materials: Default::default(),
             appearances: Default::default(),
             favorites: Default::default(),

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 {