feat: restore and persist saved camera position per layout

- On file open and layout tab switch, restore the camera from the
  document's saved view (*Active VPort for model space, sheet viewport
  for paper space) instead of fitting to wire bounds.
- After any zoom/pan/rotate, write the new camera position back to the
  document and mark the file dirty so it is saved with the file.
- Uses last_synced_camera_gen to avoid marking the file dirty on the
  initial camera restore.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/document.rs

@@ -42,6 +42,8 @@ pub(super) struct DocumentTab {
     pub(super) refedit_session: Option<RefEditSession>,
     /// Currently active MLeader style name.
     pub(super) active_mleader_style: String,
+    /// Last camera_generation value written back to the document.
+    pub(super) last_synced_camera_gen: u64,
 }
 
 impl DocumentTab {
@@ -83,6 +85,7 @@ impl DocumentTab {
             paper_bg_color: None,
             refedit_session: None,
             active_mleader_style: "Standard".to_string(),
+            last_synced_camera_gen: 0,
         }
     }
 

src/app/update.rs

@@ -17,7 +17,19 @@ impl H7CAD {
     pub fn update(&mut self, msg: Message) -> Task<Message> {
         match msg {
             Message::Tick(t) => {
-                self.tabs[self.active_tab].scene.update(t - self.start);
+                let i = self.active_tab;
+                self.tabs[i].scene.update(t - self.start);
+
+                // If the camera moved since we last synced, write it back to
+                // the document and mark the file dirty.
+                let gen = self.tabs[i].scene.camera_generation;
+                if gen != self.tabs[i].last_synced_camera_gen {
+                    self.tabs[i].last_synced_camera_gen = gen;
+                    if self.tabs[i].scene.sync_camera_to_document() {
+                        self.tabs[i].dirty = true;
+                    }
+                }
+
                 Task::none()
             }
 
@@ -86,7 +98,8 @@ impl H7CAD {
                 let vp_info = self.tabs[i].scene.viewport_list();
                 self.tabs[i].layers.sync_with_viewports(&doc_layers, vp_info);
                 self.sync_ribbon_layers();
-                self.tabs[i].scene.fit_all();
+                self.tabs[i].scene.restore_saved_camera();
+                self.tabs[i].last_synced_camera_gen = self.tabs[i].scene.camera_generation;
                 self.tabs[i].dirty = false;
                 self.tabs[i].history = super::document::HistoryState::default();
                 self.refresh_selected_grips();
@@ -2249,7 +2262,8 @@ impl H7CAD {
                 self.tabs[i].scene.active_viewport = None;
                 self.tabs[i].scene.current_layout = name;
                 self.tabs[i].scene.deselect_all();
-                self.tabs[i].scene.fit_all();
+                self.tabs[i].scene.restore_saved_camera();
+                self.tabs[i].last_synced_camera_gen = self.tabs[i].scene.camera_generation;
                 if going_to_paper {
                     if let Some(idx) = self.ribbon.layout_module_index() {
                         self.ribbon.select(idx);