fix: selection toolbar/handles track scroll viewport like TextField

CHANGELOG.md

@@ -14,6 +14,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fixed an issue where bullet points became visually detached from the text body when toggling text direction formatting (RTL) by locking the list leading block to the editor's base text direction.
 - Fixed typed text being inserted at the previous caret position on Android after moving the caret with a tap/mouse by keeping the platform IME's editing state in sync with the selection even when the keyboard is hidden.
+- Selection handles and Cut/Copy/Paste toolbar now track the scroll viewport like a multiline `TextField`: handles fade when scrolled out of view, and the context menu hides while scrolling (restored if the selection is still visible).
+- Context menu anchors are clamped into the visible editor region when the selection extends past the viewport.
+- Context menu is shown again after selection-handle drag ends (or a handle tap), matching `TextField` behavior.
 
 ### Removed
 

lib/src/editor/editor.dart

@@ -726,13 +726,34 @@ class RenderEditor extends RenderEditableContainerBox
   ValueListenable<bool> get selectionEndInViewport => _selectionEndInViewport;
   final ValueNotifier<bool> _selectionEndInViewport = ValueNotifier<bool>(true);
 
+  /// Visible area of this editor in local coordinates.
+  ///
+  /// When the editor is inside a [Scrollable] (e.g. [SingleChildScrollView]),
+  /// [size] is the full document — not the on-screen window. Using the ancestor
+  /// viewport matches [RenderEditable] / multiline [TextField] behavior so
+  /// selection handles fade when scrolled out of view.
+  Rect _localVisibleRegion() {
+    final abstractViewport = RenderAbstractViewport.maybeOf(this);
+    if (abstractViewport is! RenderBox) {
+      return Offset.zero & size;
+    }
+    final viewport = abstractViewport as RenderBox;
+    if (!viewport.hasSize || !hasSize) {
+      return Offset.zero & size;
+    }
+    final topLeft = globalToLocal(viewport.localToGlobal(Offset.zero));
+    final rect = topLeft & viewport.size;
+    if (!rect.isEmpty &&
+        rect.width.isFinite &&
+        rect.height.isFinite &&
+        rect.left <= rect.right &&
+        rect.top <= rect.bottom) {
+      return rect;
+    }
+    return Offset.zero & size;
+  }
+
   void _updateSelectionExtentsVisibility(Offset effectiveOffset) {
-    final visibleRegion = Offset.zero & size;
-    final startPosition = TextPosition(
-      offset: selection.start,
-      affinity: selection.affinity,
-    );
-    final startOffset = _getOffsetForCaret(startPosition);
     // TODO(justinmc): https://github.com/flutter/flutter/issues/31495
     // Check if the selection is visible with an approximation because a
     // difference between rounded and unrounded values causes the caret to be
@@ -741,18 +762,37 @@ class RenderEditor extends RenderEditableContainerBox
     // _applyFloatingPointHack. Ideally, the rounding mismatch will be fixed and
     // this can be changed to be a strict check instead of an approximation.
     const visibleRegionSlop = 0.5;
-    _selectionStartInViewport.value = visibleRegion
-        .inflate(visibleRegionSlop)
-        .contains(startOffset + effectiveOffset);
 
-    final endPosition = TextPosition(
-      offset: selection.end,
-      affinity: selection.affinity,
-    );
+    final abstractViewport = RenderAbstractViewport.maybeOf(this);
+    final Rect visibleRegion;
+    final Offset pointOffset;
+    if (abstractViewport is RenderBox) {
+      final viewport = abstractViewport as RenderBox;
+      if (viewport.hasSize) {
+        // Viewport-relative check: caret offsets are already in local document
+        // space; do not apply [effectiveOffset] again.
+        visibleRegion = _localVisibleRegion().inflate(visibleRegionSlop);
+        pointOffset = Offset.zero;
+      } else {
+        visibleRegion = (Offset.zero & size).inflate(visibleRegionSlop);
+        pointOffset = effectiveOffset;
+      }
+    } else {
+      visibleRegion = (Offset.zero & size).inflate(visibleRegionSlop);
+      pointOffset = effectiveOffset;
+    }
+
+    final startPosition =
+        TextPosition(offset: selection.start, affinity: selection.affinity);
+    final startOffset = _getOffsetForCaret(startPosition);
+    _selectionStartInViewport.value =
+        visibleRegion.contains(startOffset + pointOffset);
+
+    final endPosition =
+        TextPosition(offset: selection.end, affinity: selection.affinity);
     final endOffset = _getOffsetForCaret(endPosition);
-    _selectionEndInViewport.value = visibleRegion
-        .inflate(visibleRegionSlop)
-        .contains(endOffset + effectiveOffset);
+    _selectionEndInViewport.value =
+        visibleRegion.contains(endOffset + pointOffset);
   }
 
   // returns offset relative to this at which the caret will be painted
@@ -1219,10 +1259,13 @@ class RenderEditor extends RenderEditableContainerBox
     PaintingContext context,
     List<TextSelectionPoint> endpoints,
   ) {
+    // Clamp into the on-screen region (viewport), not the full document size,
+    // matching RenderEditable when the editable itself is the scroll viewport.
+    final visible = _localVisibleRegion();
     var startPoint = endpoints[0].point;
     startPoint = Offset(
-      startPoint.dx.clamp(0.0, size.width),
-      startPoint.dy.clamp(0.0, size.height),
+      startPoint.dx.clamp(visible.left, visible.right),
+      startPoint.dy.clamp(visible.top, visible.bottom),
     );
     context.pushLayer(
       LeaderLayer(link: _startHandleLayerLink, offset: startPoint),
@@ -1232,8 +1275,8 @@ class RenderEditor extends RenderEditableContainerBox
     if (endpoints.length == 2) {
       var endPoint = endpoints[1].point;
       endPoint = Offset(
-        endPoint.dx.clamp(0.0, size.width),
-        endPoint.dy.clamp(0.0, size.height),
+        endPoint.dx.clamp(visible.left, visible.right),
+        endPoint.dy.clamp(visible.top, visible.bottom),
       );
       context.pushLayer(
         LeaderLayer(link: _endHandleLayerLink, offset: endPoint),