fix: drawing tools sync issue in mobile app

lib/src/add_ons/add_ons_repository.dart

@@ -3,6 +3,7 @@ import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
 import 'package:deriv_chart/src/add_ons/add_on_config.dart';
 import 'package:deriv_chart/src/add_ons/repository.dart';
+import 'package:deriv_chart/src/misc/chart_diagnostics.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
 /// Called to create an AddOnConfig object from a map.
@@ -73,6 +74,9 @@ class AddOnsRepository<T extends AddOnConfig> extends ChangeNotifier
 
     if (!prefs.containsKey(addOnsKey)) {
       // No saved indicators or drawing tools.
+      if (kChartDiagnosticsEnabled) {
+        chartDiag('repo#$hashCode loadFromPrefs($addOnsKey): no saved items');
+      }
       notifyListeners();
       return;
     }
@@ -90,6 +94,11 @@ class AddOnsRepository<T extends AddOnConfig> extends ChangeNotifier
       _hiddenStatus.add(false);
     }
 
+    if (kChartDiagnosticsEnabled) {
+      chartDiag('repo#$hashCode loadFromPrefs($addOnsKey): loaded '
+          '${items.map((T c) => c.configId).toList()}');
+    }
+
     notifyListeners();
   }
 
@@ -98,6 +107,10 @@ class AddOnsRepository<T extends AddOnConfig> extends ChangeNotifier
   void add(T addOnConfig) {
     items.add(addOnConfig);
     _hiddenStatus.add(false);
+    if (kChartDiagnosticsEnabled) {
+      chartDiag('repo#$hashCode add(${addOnConfig.configId}) -> $addOnsKey, '
+          'items: ${items.map((T c) => c.configId).toList()}');
+    }
     _writeToPrefs();
     notifyListeners();
   }
@@ -128,6 +141,11 @@ class AddOnsRepository<T extends AddOnConfig> extends ChangeNotifier
     }
     final removedItem = items.removeAt(index);
     _hiddenStatus.removeAt(index);
+    if (kChartDiagnosticsEnabled) {
+      chartDiag('repo#$hashCode removeAt($index) '
+          'removed ${removedItem.configId} -> $addOnsKey, '
+          'items: ${items.map((T c) => c.configId).toList()}');
+    }
     _writeToPrefs();
     // Notify about the deletion
     onDeleteCallback?.call(removedItem, index);
@@ -148,6 +166,9 @@ class AddOnsRepository<T extends AddOnConfig> extends ChangeNotifier
   void clear() {
     items.clear();
     _hiddenStatus.clear();
+    if (kChartDiagnosticsEnabled) {
+      chartDiag('repo#$hashCode clear() -> $addOnsKey');
+    }
     _writeToPrefs();
     notifyListeners();
   }

lib/src/deriv_chart/chart/main_chart.dart

@@ -511,38 +511,43 @@ class _ChartImplementationState extends BasicChartState<MainChart> {
         loadingAnimationColor: widget.loadingAnimationColor,
       );
 
-  Widget _buildAnnotations() => MultipleAnimatedBuilder(
-        animations: <Animation<double>>[
-          currentTickAnimation,
-          _currentTickBlinkAnimation,
-          topBoundQuoteAnimationController,
-          bottomBoundQuoteAnimationController,
-        ],
-        builder: (BuildContext context, _) =>
-            Stack(fit: StackFit.expand, children: <Widget>[
-          if (widget.annotations != null)
-            ...widget.annotations!
-                .map(
-                  (ChartData annotation) => RepaintBoundary(
-                    child: CustomPaint(
-                      key: ValueKey<String>(annotation.id),
-                      painter: ChartPainter(
-                        animationInfo: AnimationInfo(
-                          currentTickPercent: currentTickAnimation.value,
-                          blinkingPercent: _currentTickBlinkAnimation.value,
+  Widget _buildAnnotations() => LayoutBuilder(
+        builder: (BuildContext context, BoxConstraints constraints) {
+          final XAxisModel xAxisModel = context.watch<XAxisModel>();
+          return MultipleAnimatedBuilder(
+            animations: <Listenable>[
+              currentTickAnimation,
+              _currentTickBlinkAnimation,
+              topBoundQuoteAnimationController,
+              bottomBoundQuoteAnimationController,
+            ],
+            builder: (BuildContext context, _) =>
+                Stack(fit: StackFit.expand, children: <Widget>[
+              if (widget.annotations != null)
+                ...widget.annotations!
+                    .map(
+                      (ChartData annotation) => RepaintBoundary(
+                        child: CustomPaint(
+                          key: ValueKey<String>(annotation.id),
+                          painter: ChartPainter(
+                            animationInfo: AnimationInfo(
+                              currentTickPercent: currentTickAnimation.value,
+                              blinkingPercent: _currentTickBlinkAnimation.value,
+                            ),
+                            chartData: annotation,
+                            chartConfig: context.watch<ChartConfig>(),
+                            theme: context.watch<ChartTheme>(),
+                            epochToCanvasX: xAxisModel.xFromEpoch,
+                            quoteToCanvasY: chartQuoteToCanvasY,
+                            chartScaleModel: context.watch<ChartScaleModel>(),
+                          ),
                         ),
-                        chartData: annotation,
-                        chartConfig: context.watch<ChartConfig>(),
-                        theme: context.watch<ChartTheme>(),
-                        epochToCanvasX: xAxis.xFromEpoch,
-                        quoteToCanvasY: chartQuoteToCanvasY,
-                        chartScaleModel: context.watch<ChartScaleModel>(),
                       ),
-                    ),
-                  ),
-                )
-                .toList()
-        ]),
+                    )
+                    .toList()
+            ]),
+          );
+        },
       );
 
   Widget _buildScrollToLastTickButton() => Material(
@@ -590,13 +595,26 @@ class _ChartImplementationState extends BasicChartState<MainChart> {
           topBoundQuoteAnimationController,
           bottomBoundQuoteAnimationController
         ],
-        builder: (BuildContext context, _) => MarkerArea(
-          markerSeries: widget.markerSeries!,
-          quoteToCanvasY: chartQuoteToCanvasY,
-          animationInfo: AnimationInfo(
-            currentTickPercent: currentTickAnimation.value,
-          ),
-        ),
+        builder: (BuildContext context, _) {
+          // This builder re-runs on every animation tick, independently of the
+          // gating LayoutBuilder. During a trade-type switch / navigation the
+          // series can become null while the animation controllers are still
+          // ticking (e.g. a running contract), so we must NOT force-unwrap
+          // markerSeries here — doing so threw "Null check operator used on a
+          // null value", which Flutter rendered as the release-mode grey
+          // ErrorWidget overlaying the chart.
+          final MarkerSeries? markerSeries = widget.markerSeries;
+          if (markerSeries == null) {
+            return const SizedBox.shrink();
+          }
+          return MarkerArea(
+            markerSeries: markerSeries,
+            quoteToCanvasY: chartQuoteToCanvasY,
+            animationInfo: AnimationInfo(
+              currentTickPercent: currentTickAnimation.value,
+            ),
+          );
+        },
       );
 
   Widget _buildDataFitButton() {