test: highlighter-kind + single-finger-pan widget guards

Two more device-independent live-path guards: the highlighter tool commits a
PenStrokeKind.highlighter stroke; a single finger PANS the shared transform
(translation changes) when finger-drawing is off and does NOT draw — the
touch→pan vs stylus→draw split.

flutter analyze lib/editor clean; 240/240 tests (+2).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/pen_tool_widget_test.dart

@@ -0,0 +1,92 @@
+// Device-independent guards for two more live-path behaviors: the highlighter
+// tool produces a highlighter-kind stroke, and a single finger PANS the shared
+// transform when finger-drawing is off (touch → pan, not draw).
+
+import 'package:flutter/gestures.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:badnote/editor/canvas/pen_canvas.dart';
+import 'package:badnote/editor/canvas/pen_stroke.dart';
+
+void main() {
+  const pageSize = Size(400, 600);
+
+  Widget host({
+    required void Function(PenStroke) onComplete,
+    required TransformationController controller,
+    CanvasTool tool = CanvasTool.pen,
+    bool allowFinger = false,
+  }) =>
+      MaterialApp(
+        home: Scaffold(
+          body: Center(
+            child: SizedBox(
+              width: pageSize.width,
+              height: pageSize.height,
+              child: PenCanvas(
+                pageWidget: Container(color: const Color(0xFFEEEEEE)),
+                pageSize: pageSize,
+                strokes: const <PenStroke>[],
+                transformationController: controller,
+                tool: tool,
+                color: const Color(0xFFFF0000),
+                strokeWidth: 0.02,
+                allowFingerDrawing: allowFinger,
+                onStrokeComplete: onComplete,
+                onEraseStroke: (_, __) {},
+              ),
+            ),
+          ),
+        ),
+      );
+
+  testWidgets('highlighter tool commits a highlighter-kind stroke',
+      (tester) async {
+    final committed = <PenStroke>[];
+    final controller = TransformationController();
+    addTearDown(controller.dispose);
+
+    await tester.pumpWidget(host(
+      onComplete: committed.add,
+      controller: controller,
+      tool: CanvasTool.highlighter,
+    ));
+
+    final center = tester.getCenter(find.byType(PenCanvas));
+    final g = await tester.startGesture(center, kind: PointerDeviceKind.stylus);
+    await g.moveBy(const Offset(30, 0));
+    await g.up();
+    await tester.pump();
+
+    expect(committed, hasLength(1));
+    expect(committed.single.kind, PenStrokeKind.highlighter);
+  });
+
+  testWidgets('a single finger PANS the transform when finger-drawing is off',
+      (tester) async {
+    final committed = <PenStroke>[];
+    final controller = TransformationController();
+    addTearDown(controller.dispose);
+
+    await tester.pumpWidget(host(
+      onComplete: committed.add,
+      controller: controller,
+      allowFinger: false,
+    ));
+
+    final before = controller.value.getTranslation();
+    final center = tester.getCenter(find.byType(PenCanvas));
+    final g = await tester.startGesture(center, kind: PointerDeviceKind.touch);
+    await g.moveBy(const Offset(40, 25));
+    await g.moveBy(const Offset(20, 15));
+    await g.up();
+    await tester.pump();
+
+    final after = controller.value.getTranslation();
+    // It panned (translation changed) and did NOT draw.
+    expect((after.x - before.x).abs() + (after.y - before.y).abs(),
+        greaterThan(1.0));
+    expect(committed, isEmpty);
+  });
+}