Only save annotations on changes

lib/features/sheet_viewer/sheet_viewer_page.dart

@@ -103,7 +103,7 @@ class _SheetViewerPageState extends State<SheetViewerPage>
     });
 
     // Sync annotations from server (downloads newer versions)
-    await _syncService.syncAnnotationsFromServer(widget.sheet.uuid);
+    await _syncService.syncFromServer(widget.sheet.uuid);
 
     // Load annotations for current page(s)
     await _loadAnnotationsForCurrentPages();
@@ -143,32 +143,40 @@ class _SheetViewerPageState extends State<SheetViewerPage>
   }
 
   /// Saves the current page(s) annotations to storage and uploads to server.
+  ///
+  /// Only saves if there are actual changes to avoid unnecessary writes/uploads.
   Future<void> _saveCurrentAnnotations() async {
     final now = DateTime.now();
 
-    // Save left page
-    final leftJson = _leftDrawingController.toJsonString();
-    final leftHasContent = leftJson.isNotEmpty && leftJson != '[]';
+    // Save left page only if changed
+    if (_leftDrawingController.hasUnsavedChanges) {
+      final leftJson = _leftDrawingController.toJsonString();
+      final leftHasContent = leftJson.isNotEmpty && leftJson != '[]';
 
-    await _storageService.writeAnnotationsWithMetadata(
-      widget.sheet.uuid,
-      _currentPage,
-      leftHasContent ? leftJson : null,
-      now,
-    );
-
-    // Upload left page to server
-    if (leftHasContent) {
-      _syncService.uploadAnnotation(
-        sheetUuid: widget.sheet.uuid,
-        page: _currentPage,
-        annotationsJson: leftJson,
-        lastModified: now,
+      await _storageService.writeAnnotationsWithMetadata(
+        widget.sheet.uuid,
+        _currentPage,
+        leftHasContent ? leftJson : null,
+        now,
       );
+
+      // Upload left page to server
+      if (leftHasContent) {
+        _syncService.uploadAnnotation(
+          sheetUuid: widget.sheet.uuid,
+          page: _currentPage,
+          annotationsJson: leftJson,
+          lastModified: now,
+        );
+      }
+
+      _leftDrawingController.markSaved();
     }
 
-    // Save right page (two-page mode)
-    if (widget.config.twoPageMode && _currentPage < _totalPages) {
+    // Save right page (two-page mode) only if changed
+    if (widget.config.twoPageMode &&
+        _currentPage < _totalPages &&
+        _rightDrawingController.hasUnsavedChanges) {
       final rightJson = _rightDrawingController.toJsonString();
       final rightHasContent = rightJson.isNotEmpty && rightJson != '[]';
 
@@ -188,6 +196,8 @@ class _SheetViewerPageState extends State<SheetViewerPage>
           lastModified: now,
         );
       }
+
+      _rightDrawingController.markSaved();
     }
   }
 
@@ -290,9 +300,8 @@ class _SheetViewerPageState extends State<SheetViewerPage>
           icon: Icon(
             widget.config.fullscreen ? Icons.fullscreen_exit : Icons.fullscreen,
           ),
-          tooltip: widget.config.fullscreen
-              ? 'Exit Fullscreen'
-              : 'Enter Fullscreen',
+          tooltip:
+              widget.config.fullscreen ? 'Exit Fullscreen' : 'Enter Fullscreen',
           onPressed: _toggleFullscreen,
         ),
         IconButton(
@@ -304,9 +313,8 @@ class _SheetViewerPageState extends State<SheetViewerPage>
           icon: Icon(
             widget.config.twoPageMode ? Icons.filter_1 : Icons.filter_2,
           ),
-          tooltip: widget.config.twoPageMode
-              ? 'Single Page Mode'
-              : 'Two Page Mode',
+          tooltip:
+              widget.config.twoPageMode ? 'Single Page Mode' : 'Two Page Mode',
           onPressed: _toggleTwoPageMode,
         ),
       ],
@@ -338,9 +346,8 @@ class _SheetViewerPageState extends State<SheetViewerPage>
       currentPageNumber: _currentPage,
       config: widget.config,
       leftDrawingController: _leftDrawingController,
-      rightDrawingController: widget.config.twoPageMode
-          ? _rightDrawingController
-          : null,
+      rightDrawingController:
+          widget.config.twoPageMode ? _rightDrawingController : null,
       drawingEnabled: _isPaintMode,
     );