fix(extend): use preselected objects as boundary edges

TRIM already takes objects selected before the command as cutting
edges; EXTEND ignored them and extended to the nearest object in the
path. It now takes them as boundary edges the same way.

Fixes #1732

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/commands/dim.rs

@@ -1386,8 +1386,17 @@ impl OpenCADStudio {
                             .map(|e| (h, e))
                     })
                     .collect();
+                let initial_edges: Vec<codec::Handle> = self.tabs[i]
+                    .scene
+                    .selected_entities()
+                    .into_iter()
+                    .filter_map(|(handle, entity)| {
+                        crate::modules::draw::modify::trim::is_trim_boundary_entity(&entity)
+                            .then_some(handle)
+                    })
+                    .collect();
                 let all_entities: Vec<_> = entities.into_iter().map(|(_, e)| e).collect();
-                let new_cmd = ExtendCommand::new(all_entities);
+                let new_cmd = ExtendCommand::with_boundary_edges(all_entities, initial_edges);
                 self.command_line.push_info(&new_cmd.prompt());
                 self.tabs[i].active_cmd = Some(Box::new(new_cmd));
             }

src/modules/draw/modify/trim.rs

@@ -3358,21 +3358,28 @@ pub struct ExtendCommand {
 
 impl ExtendCommand {
     pub fn new(all_entities: Vec<EntityType>) -> Self {
+        Self::with_boundary_edges(all_entities, Vec::new())
+    }
+
+    /// Objects selected before the command are its boundary edges, as TRIM
+    /// takes them as cutting edges.
+    pub fn with_boundary_edges(all_entities: Vec<EntityType>, initial_edges: Vec<Handle>) -> Self {
         let all_entities: Vec<EntityType> = all_entities
             .iter()
             .map(entity_with_lwpolyline_world_xy)
             .collect();
         let entity_index = ModifyEntityIndex::build(&all_entities);
-        let geos = build_geos(&all_entities);
-        Self {
+        let mut cmd = Self {
             all_entities,
             entity_index,
-            geos,
+            geos: Vec::new(),
             mode: TrimMode::Pick,
-            edge_set: Vec::new(),
+            edge_set: initial_edges,
             implied_edges: false,
             shift: false,
-        }
+        };
+        cmd.rebuild_geos();
+        cmd
     }
 
     fn rebuild_geos(&mut self) {