fix(blocks): enforce constant attributes in ATTEDIT and restore ATTDEFs on explode

Enforce constant attribute flag in ATTEDIT dialog by presenting constant attributes as disabled and ignoring modifications. When exploding an insert, restore block-definition attribute definitions as transformed ATTDEF entities while dropping instance attribute values.

src/modules/draw/modify/explode.rs

@@ -115,18 +115,49 @@ pub fn explode_entity(entity: &EntityType, document: &CadDocument) -> Vec<Entity
                 // contents, not on the insert.
                 let base = crate::scene::render_graph::block_base_point(document, &ins.block_name);
                 let to_block = Transform::from_translation(Vector3::new(-base.x, -base.y, -base.z));
+                let mut attdefs: Vec<EntityType> = Vec::new();
                 let entities: Vec<EntityType> = document
                     .entities_in_block(&ins.block_name)
                     .map(|entity| {
                         let mut shifted = entity.clone();
                         Entity::apply_transform(shifted.as_entity_mut(), &to_block);
+                        if let EntityType::AttributeDefinition(_) = &shifted {
+                            attdefs.push(shifted.clone());
+                        }
                         shifted
                     })
                     .collect();
-                ins.explode(&entities)
+                let mut pieces: Vec<EntityType> = ins
+                    .explode(&entities)
                     .into_iter()
                     .map(normalize_insert_entity)
-                    .collect()
+                    .collect();
+
+                // Exploding an INSERT drops attribute values (ATTRIBs)
+                // and the attribute definitions (ATTDEF tags) reappear as ATTDEF entities.
+                // The codec's `ins.explode` skips `AttributeDefinition` entities, so we
+                // transform and append them here.
+                if !attdefs.is_empty() {
+                    let insert_xform = ins.get_transform();
+                    for ad_ent in &attdefs {
+                        let mut exploded_ad = ad_ent.clone();
+                        Entity::apply_transform(exploded_ad.as_entity_mut(), &insert_xform);
+                        // Resolve common properties (layer "0", ByBlock color / line weight)
+                        let common = exploded_ad.common_mut();
+                        if common.layer == "0" {
+                            common.layer = ins.common.layer.clone();
+                        }
+                        if common.color == codec::types::Color::ByBlock {
+                            common.color = ins.common.color;
+                        }
+                        if common.line_weight == codec::types::LineWeight::ByBlock {
+                            common.line_weight = ins.common.line_weight;
+                        }
+                        pieces.push(exploded_ad);
+                    }
+                }
+
+                pieces
             }
         }
         EntityType::MLine(ml) => explode_mline(ml),