feat(layout): reopen a drawing in the space it was saved in

Files saved while a paper layout was active reopened in Model space
because the loader hardcoded the current layout to "Model" and never
consulted the space recorded in the file.

The active space is a standard part of the format and acadrust already
round-trips it: $TILEMODE (header.show_model_space) for model-vs-paper,
and the CTAB current-tab variable for the exact layout name.

- Read: on open, pick the current layout from CTAB (when it names a
  layout that exists), else $TILEMODE (Model, or the first paper layout).
- Write: Scene::sync_active_space_to_document() mirrors the active layout
  back into the document (show_model_space + CTAB). It runs from
  set_current_layout, so every active-layout change — the status-bar tab,
  the Layout Manager's Set Current, create / rename / delete, and
  undo/redo — keeps the document in sync for the next save.

$TILEMODE is the guaranteed mechanism (read and written for both DXF and
DWG); CTAB refines the exact tab when the variable is present.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/app/update/file.rs

@@ -489,7 +489,28 @@ pub(super) fn on_open_file(&mut self) -> Task<Message> {
                 }
                 self.tabs[i].scene.selected = rustc_hash::FxHashSet::default();
                 self.tabs[i].scene.preview_wires = vec![];
-                self.tabs[i].scene.current_layout = "Model".to_string();
+                // Reopen in whichever space the file was saved in — the CTAB
+                // tab name when recorded, else the $TILEMODE model/paper flag —
+                // instead of always landing in Model.
+                {
+                    let names = self.tabs[i].scene.layout_names();
+                    let saved = crate::io::saved_active_layout(&self.tabs[i].scene.document)
+                        .and_then(|n| {
+                            names.iter().find(|x| x.eq_ignore_ascii_case(&n)).cloned()
+                        });
+                    self.tabs[i].scene.current_layout = match saved {
+                        Some(n) => n,
+                        None if self.tabs[i].scene.document.header.show_model_space => {
+                            "Model".to_string()
+                        }
+                        // Paper was active but no CTAB — fall back to the first
+                        // paper layout (names[0] is always "Model").
+                        None => names
+                            .into_iter()
+                            .nth(1)
+                            .unwrap_or_else(|| "Model".to_string()),
+                    };
+                }
                 // Rebuild the Isolate/Hide set from the entities the file itself
                 // marks invisible (DXF code 60), so hidden objects stay hidden on
                 // reopen and End Isolation can bring them back.

src/app/update/mod.rs

@@ -2569,7 +2569,7 @@ impl OpenCADStudio {
                     self.push_undo_snapshot(i, "LAYOUT RENAME");
                     self.tabs[i].scene.rename_layout(&old_name, &new_name);
                     if self.tabs[i].scene.current_layout == old_name {
-                        self.tabs[i].scene.current_layout = new_name.clone();
+                        self.tabs[i].scene.set_current_layout(new_name.clone());
                     }
                     self.layout_manager_selected = new_name.clone();
                     self.tabs[i].dirty = true;
@@ -2610,8 +2610,7 @@ impl OpenCADStudio {
                     self.tabs[i].dirty = true;
                     // Switch to Model if active layout was deleted.
                     if self.tabs[i].scene.current_layout == name {
-                        self.tabs[i].scene.current_layout = "Model".to_string();
-                        self.tabs[i].scene.bump_geometry();
+                        self.tabs[i].scene.set_current_layout("Model".to_string());
                     }
                     self.layout_manager_selected = "Model".to_string();
                     self.layout_manager_rename_buf = String::new();
@@ -2658,8 +2657,7 @@ impl OpenCADStudio {
             Message::LayoutManagerSetCurrent => {
                 let i = self.active_tab;
                 let name = self.layout_manager_selected.clone();
-                self.tabs[i].scene.current_layout = name.clone();
-                self.tabs[i].scene.bump_geometry();
+                self.tabs[i].scene.set_current_layout(name.clone());
                 self.command_line
                     .push_output(&format!("Switched to layout '{name}'."));
                 Task::none()

src/app/update/viewport.rs

@@ -3050,7 +3050,7 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                                 }
                             }
                         }
-                        self.tabs[i].scene.current_layout = new_name.clone();
+                        self.tabs[i].scene.set_current_layout(new_name.clone());
                         // Safety net — `add_layout` already creates the overall
                         // sheet viewport; this covers any path that doesn't.
                         self.tabs[i].scene.ensure_sheet_viewport(&new_name);
@@ -3085,7 +3085,7 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                             self.push_undo_snapshot(i, "LAYOUT RENAME");
                             self.tabs[i].scene.rename_layout(&orig, &new_name);
                             if self.tabs[i].scene.current_layout == orig {
-                                self.tabs[i].scene.current_layout = new_name.clone();
+                                self.tabs[i].scene.set_current_layout(new_name.clone());
                             }
                             self.tabs[i].dirty = true;
                             self.command_line