fix(group): preserve groups when pasting, cross-drawing too

PR #446 kept a fully-copied group grouped for the in-drawing COPY/ARRAY
path, but clipboard paste (Ctrl+C / Ctrl+V, PASTECLIP) runs through
finalize_paste, a separate route that never touched groups — so pasted
copies came out ungrouped, and a cross-drawing paste had no group data at
all.

Unify all copy routes on one shared Scene::recreate_groups(sources,
handle_map): copy_complete_groups now gathers the live source groups and
delegates to it, while paste snapshots the complete groups into the
clipboard at copy time (ClipboardDeps.groups) and recreates them over the
pasted handles. A group whose whole membership is copied now stays grouped
whether the copy lands in the same drawing, via the clipboard, or in a
different file; partially-selected groups still stay ungrouped.

Closes #440

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/mod.rs

@@ -886,6 +886,12 @@ pub struct ClipboardDeps {
     /// `xdictionary` graph is snapshotted so a cross-drawing paste recreates it
     /// — without this a pasted clipped block loses its clip and renders whole.
     pub ext_objects: Vec<ClipExtObjects>,
+    /// Groups whose *entire* membership is in the copied selection, snapshotted
+    /// from the source drawing. On paste each is recreated over the pasted
+    /// handles so a copied group stays grouped — cross-drawing too, the same way
+    /// the in-drawing COPY path preserves it. Partly-selected groups are not
+    /// captured (copying one member should not spawn a fragment). See #440.
+    pub groups: Vec<acadrust::objects::Group>,
 }
 
 /// A captured block definition: its base point and the entities it owns
@@ -1001,6 +1007,25 @@ impl ClipboardDeps {
             .filter_map(|n| Self::snapshot_block(doc, n))
             .collect();
 
+        // Groups fully contained in the top-level selection. Groups reference
+        // top-level entities (not block internals), so match against `entities`
+        // only. Mirrors the in-drawing `copy_complete_groups` membership test.
+        let copied_handles: rustc_hash::FxHashSet<acadrust::Handle> =
+            entities.iter().map(|e| e.common().handle).collect();
+        let groups: Vec<acadrust::objects::Group> = doc
+            .objects
+            .values()
+            .filter_map(|obj| match obj {
+                acadrust::objects::ObjectType::Group(g)
+                    if !g.entities.is_empty()
+                        && g.entities.iter().all(|h| copied_handles.contains(h)) =>
+                {
+                    Some(g.clone())
+                }
+                _ => None,
+            })
+            .collect();
+
         ClipboardDeps {
             layers: layers
                 .iter()
@@ -1021,6 +1046,7 @@ impl ClipboardDeps {
             blocks,
             dim_blocks,
             ext_objects,
+            groups,
         }
     }