fix(ui): improve cross-platform text input behavior (#1477)

ui/flutter/lib/shared/widgets/app_http_headers_editor.dart

@@ -5,6 +5,7 @@ import 'package:shadcn_flutter/shadcn_flutter.dart' as shad;
 import '../theme/app_design_tokens.dart';
 import '../theme/app_palette.dart';
 import '../../l10n/l10n.dart';
+import 'app_text_field.dart';
 
 class AppHttpHeadersController extends ChangeNotifier {
   AppHttpHeadersController({Map<String, String>? headers, Iterable<String> defaultNames = const []}) {
@@ -171,7 +172,7 @@ class _HeaderTextField extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final palette = AppPalette.of(context);
-    return shad.TextField(
+    return AppTextField(
       controller: controller,
       hintText: hintText,
       filled: true,

ui/flutter/lib/shared/widgets/app_loading_button.dart

@@ -38,7 +38,7 @@ class AppLoadingButton extends StatelessWidget {
             children: [
               leading,
               const SizedBox(width: AppDesignTokens.space8),
-              effectiveChild,
+              Flexible(child: effectiveChild),
             ],
           );
     final effectiveOnPressed = loading ? null : onPressed;

ui/flutter/lib/shared/widgets/app_number_input.dart

@@ -2,6 +2,8 @@ import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 import 'package:shadcn_flutter/shadcn_flutter.dart' as shad;
 
+import 'app_text_field.dart';
+
 /// A bounded numeric text field with the app's standard spinner controls.
 class AppNumberInput extends StatefulWidget {
   const AppNumberInput({
@@ -80,7 +82,7 @@ class _AppNumberInputState extends State<AppNumberInput> {
             FilteringTextInputFormatter.digitsOnly,
             _NumericalRangeFormatter(min: widget.min.toInt(), max: widget.max?.toInt()),
           ];
-    return shad.TextField(
+    return AppTextField(
       key: widget.fieldKey,
       controller: widget.controller,
       hintText: widget.hintText,

ui/flutter/lib/shared/widgets/app_path_picker_field.dart

@@ -4,6 +4,7 @@ import 'package:shadcn_flutter/shadcn_flutter.dart' as shad;
 
 import '../../core/utils/breakpoints.dart';
 import '../services/download_directory_picker.dart';
+import 'app_text_field.dart';
 import 'app_tooltip.dart';
 
 enum AppPathPickerButtonStyle { ghost, outline }
@@ -119,7 +120,7 @@ class _AppPathPickerFieldState extends State<AppPathPickerField> {
               onEnter: (_) => _syncTooltipPath(),
               child: AppTooltip(
                 message: _tooltipPath,
-                child: shad.TextField(
+                child: AppTextField(
                   key: widget.fieldKey,
                   controller: widget.controller,
                   hintText: widget.hintText,

ui/flutter/lib/shared/widgets/app_text_field.dart

@@ -0,0 +1,99 @@
+import 'package:flutter/material.dart' as material show AdaptiveTextSelectionToolbar;
+import 'package:flutter/widgets.dart';
+import 'package:shadcn_flutter/shadcn_flutter.dart' as shad;
+
+/// The app-wide text field.
+///
+/// shadcn_flutter's custom context menu is rendered in a full-screen overlay
+/// that can cover the app with an opaque surface. Use Flutter's adaptive
+/// platform toolbar everywhere so long-press and right-click text actions have
+/// consistent native behavior on mobile, desktop, and web.
+class AppTextField extends shad.TextField {
+  const AppTextField({
+    super.key,
+    super.groupId,
+    super.controller,
+    super.initialValue,
+    super.focusNode,
+    super.undoController,
+    super.decoration,
+    super.padding,
+    super.placeholder,
+    super.crossAxisAlignment,
+    super.clearButtonSemanticLabel,
+    super.keyboardType,
+    super.textInputAction,
+    super.textCapitalization,
+    super.style,
+    super.strutStyle,
+    super.textAlign,
+    super.textAlignVertical,
+    super.textDirection,
+    super.readOnly,
+    super.showCursor,
+    super.autofocus,
+    super.obscuringCharacter,
+    super.obscureText,
+    super.autocorrect,
+    super.smartDashesType,
+    super.smartQuotesType,
+    super.enableSuggestions,
+    super.maxLines,
+    super.minLines,
+    super.expands,
+    super.maxLength,
+    super.maxLengthEnforcement,
+    super.onChanged,
+    super.onEditingComplete,
+    super.onSubmitted,
+    super.onTapOutside,
+    super.onTapUpOutside,
+    super.inputFormatters,
+    super.enabled,
+    super.cursorWidth,
+    super.cursorHeight,
+    super.cursorRadius,
+    super.cursorOpacityAnimates,
+    super.cursorColor,
+    super.selectionHeightStyle,
+    super.selectionWidthStyle,
+    super.keyboardAppearance,
+    super.scrollPadding,
+    super.enableInteractiveSelection,
+    super.selectionControls,
+    super.dragStartBehavior,
+    super.scrollController,
+    super.scrollPhysics,
+    super.onTap,
+    super.autofillHints,
+    super.clipBehavior,
+    super.restorationId,
+    super.stylusHandwritingEnabled,
+    super.enableIMEPersonalizedLearning,
+    super.contentInsertionConfiguration,
+    super.contextMenuBuilder = appTextFieldContextMenuBuilder,
+    super.hintText,
+    super.border,
+    super.borderRadius,
+    super.filled,
+    super.statesController,
+    super.magnifierConfiguration,
+    super.spellCheckConfiguration,
+    super.features,
+    super.submitFormatters,
+    super.skipInputFeatureFocusTraversal,
+    super.onDragSelectionStart,
+    super.onDragSelectionUpdate,
+    super.onDragSelectionEnd,
+  });
+}
+
+Widget appTextFieldContextMenuBuilder(BuildContext context, EditableTextState editableTextState) {
+  // Match Flutter's platform text-menu policy without falling back to
+  // shadcn_flutter's full-screen overlay. EditableText bypasses this builder
+  // on Web while the browser context menu is enabled.
+  if (SystemContextMenu.isSupportedByField(editableTextState)) {
+    return SystemContextMenu.editableText(editableTextState: editableTextState);
+  }
+  return material.AdaptiveTextSelectionToolbar.editableText(editableTextState: editableTextState);
+}