fix: long press auto-scroll speed on mobile (#1191)

* fix: long press auto-scroll speed on mobile

When long pressing and dragging on mobile, auto-scroll was too fast
because cursor drag mode used Duration.zero (instant) instead of
animated scrolling, and the proxy rect was a large centered square
triggering in both directions.

- Add AxisDirection.down handling in auto_scroller for directional
  proxy rects extending downward from cursor position
- Add cursor drag mode case in scroll_service_widget with direction
  detection based on cursor movement relative to last selection
- Include cursor mode in isDragOperation for animated scroll duration
- Pass dragMode in Android long press selectionExtraInfo so scroll
  service can detect cursor drag on Android

* fix: correct auto-scroller test for downward scroll rect

lib/src/editor/editor_component/service/scroll/auto_scroller.dart

@@ -50,6 +50,13 @@ class AutoScroller extends EdgeDraggingAutoScroller
       );
     }
 
+    if (direction != null && direction == AxisDirection.down) {
+      return startAutoScrollIfNecessary(
+        Rect.fromLTWH(offset.dx, offset.dy, 1, edgeOffset),
+        duration: duration,
+      );
+    }
+
     final dragTarget = Rect.fromCenter(
       center: offset,
       width: edgeOffset,

lib/src/editor/editor_component/service/scroll_service_widget.dart

@@ -121,6 +121,16 @@ class _ScrollServiceWidgetState extends State<ScrollServiceWidget>
           direction = AxisDirection.down;
           break;
 
+        case 'MobileSelectionDragMode.cursor':
+          targetRect = selectionRects.last;
+          if (lastSelection != null) {
+            final isMovingUp = selection.end.path < lastSelection!.end.path ||
+                (selection.end.path.equals(lastSelection!.end.path) &&
+                    selection.end.offset < lastSelection!.end.offset);
+            direction = isMovingUp ? AxisDirection.up : AxisDirection.down;
+          }
+          break;
+
         default:
           targetRect = selectionRects.last;
 
@@ -146,7 +156,8 @@ class _ScrollServiceWidgetState extends State<ScrollServiceWidget>
             (dragMode.toString() ==
                     'MobileSelectionDragMode.leftSelectionHandle' ||
                 dragMode.toString() ==
-                    'MobileSelectionDragMode.rightSelectionHandle');
+                    'MobileSelectionDragMode.rightSelectionHandle' ||
+                dragMode.toString() == 'MobileSelectionDragMode.cursor');
 
         // Use animation for drag operations, instant for others
         final scrollDuration =

lib/src/editor/editor_component/service/selection/mobile_selection_service.dart

@@ -787,6 +787,7 @@ class _MobileSelectionServiceWidgetState
       selection,
       reason: SelectionUpdateReason.uiEvent,
       extraInfo: {
+        selectionDragModeKey: dragMode,
         selectionExtraInfoDisableFloatingToolbar: true,
       },
     );
@@ -835,6 +836,7 @@ class _MobileSelectionServiceWidgetState
         newSelection,
         reason: SelectionUpdateReason.uiEvent,
         extraInfo: {
+          selectionDragModeKey: dragMode,
           selectionExtraInfoDisableFloatingToolbar: true,
         },
       );

test/editor/editor_component/service/auto_scroller_test.dart

@@ -102,14 +102,17 @@ void main() {
 
         expect(scroller.capturedRect, isNotNull);
 
-        // For AxisDirection.down the generic Rect.fromCenter path is used.
+        // For AxisDirection.down the rect starts at offset and extends downward.
         expect(
-          scroller.capturedRect!.center,
+          scroller.capturedRect!.top,
-          offset,
+          offset.dy,
-          reason:
+          reason: 'proxy rect should start at the handle position',
-              'right handle proxy rect should be centered on the handle offset',
+        );
+        expect(
+          scroller.capturedRect!.bottom,
+          offset.dy + edgeOffset,
+          reason: 'proxy rect should extend edgeOffset pixels BELOW the handle',
         );
-        expect(scroller.capturedRect!.width, edgeOffset);
         expect(scroller.capturedRect!.height, edgeOffset);
       },
     );