feat(diag): full input logging + read barrel from pointerFlags; focal-jump reject

Buttons (likely fix + ground truth): device diag showed ptr=12577 pen=10056 —
WM_POINTER reaches the observer and GetPointerPenInfo succeeds, so the buttons
were just read from the wrong field. Native now resolves the barrel from BOTH
penFlags(PEN_FLAG_BARREL) AND pointerInfo.pointerFlags(POINTER_FLAG_SECONDBUTTON)
— many pens use the latter. It also emits the full raw set (pointerFlags,
penFlags, penMask, ButtonChangeType, tilt) plus OR-accumulated flags so a single
session reveals exactly which field each button sets.

Comprehensive logging (per user request "用好用的log库 / 我手动开启日志再记录"):
new DiagnosticLogger emits through dart:developer log(name 'badnote.input') —
capturable via `flutter run` / DevTools / `flutter logs` — AND mirrors to a file
(path shown in the overlay) for the packaged GUI build that has no console.
Manually enabled by the toolbar diagnostic toggle; off by default. PEN lines log
on raw-field change; ZOOM lines log every scale frame + rebaselines.

Zoom: scale-only glitch rejection didn't stop the jumping, so add focal/position
glitch rejection — drop a 2-finger frame whose focal jumps >250px (a touch
misread). The full per-frame trace (raw scale, pointerCount, applied change,
focal jump, drops) is now logged so the residual cause is unambiguous.

InputDiagnostics singleton accumulates the stats; the overlay shows summary +
last trace lines + log path + reset. Removed the ad-hoc inline zoom min/max.

Dart: analyze clean, 66/66 tests, linux build green. Native compiles on CI.

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

lib/editor/canvas/pen_editor_screen.dart

@@ -12,12 +12,14 @@ import '../../services/database_service.dart';
 import '../engine/stroke_geometry.dart' show kDefaultPenThinning;
 import '../engine/stroke_model.dart';
 import '../engine/undo_stack.dart';
+import '../input/diagnostic_logger.dart';
 import '../input/pen_config.dart';
 import '../input/pen_input_service.dart';
 import '../persistence/editor_repository.dart';
 import '../persistence/save_scheduler.dart';
 import '../ui/pen_settings_page.dart';
 import '../ui/thumbnail_grid.dart';
+import 'input_diagnostics.dart';
 import 'pen_canvas.dart';
 import 'pen_stroke.dart';
 
@@ -95,13 +97,6 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
   String _penDebug = '';
   bool _showPenDebug = false;
 
-  /// Live zoom-scale diagnostic (only tracked while the overlay is on), so we
-  /// can capture the value the pinch flash jumps to. `_zoomMin/_zoomMax` record
-  /// the extremes seen since the overlay was last enabled.
-  double _zoomNow = 1.0;
-  double _zoomMin = double.infinity;
-  double _zoomMax = 0.0;
-
   // Tool state.
   CanvasTool _tool = CanvasTool.pen;
   Color _color = Colors.black;
@@ -126,23 +121,11 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
     // Begin listening to the native Windows pen plugin (barrel/eraser/tilt).
     // No-op on platforms without the plugin (W3).
     PenInputService.instance.start();
-    _transform.addListener(_onTransformDebug);
     _initPersistence();
     _initPenConfig();
     _open();
   }
 
-  /// Track the live zoom scale for the diagnostic overlay (no-op when off).
-  void _onTransformDebug() {
-    if (!_showPenDebug) return;
-    final s = _transform.value.getMaxScaleOnAxis();
-    setState(() {
-      _zoomNow = s;
-      if (s < _zoomMin) _zoomMin = s;
-      if (s > _zoomMax) _zoomMax = s;
-    });
-  }
-
   Future<void> _initPenConfig() async {
     final controller = await PenConfigController.load();
     if (!mounted) {
@@ -240,10 +223,10 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
       scheduler.dispose();
     }
     _document?.dispose();
-    _transform.removeListener(_onTransformDebug);
     _transform.dispose();
     _penConfig?.dispose();
     PenInputService.instance.stop();
+    DiagnosticLogger.instance.stop();
     super.dispose();
   }
 
@@ -453,18 +436,59 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
                   child: Material(
                     color: Theme.of(context).colorScheme.inverseSurface,
                     borderRadius: BorderRadius.circular(8),
-                    child: Padding(
-                      padding: const EdgeInsets.symmetric(
-                          horizontal: 10, vertical: 6),
-                      child: Text(
-                        '${_penDebug.isEmpty ? 'hover / draw with the pen…' : _penDebug}'
-                        '\nzoom=${_zoomNow.toStringAsFixed(2)}  '
-                        'min=${_zoomMin.isFinite ? _zoomMin.toStringAsFixed(2) : '-'}  '
-                        'max=${_zoomMax.toStringAsFixed(2)}',
-                        style: TextStyle(
-                          fontFamily: 'monospace',
-                          fontSize: 12,
-                          color: Theme.of(context).colorScheme.onInverseSurface,
+                    child: ConstrainedBox(
+                      constraints: const BoxConstraints(maxWidth: 380),
+                      child: Padding(
+                        padding: const EdgeInsets.symmetric(
+                            horizontal: 10, vertical: 6),
+                        child: ListenableBuilder(
+                          listenable: InputDiagnostics.instance,
+                          builder: (context, _) {
+                            final cs = Theme.of(context).colorScheme;
+                            final d = InputDiagnostics.instance;
+                            final tail = d.trace.length > 6
+                                ? d.trace.sublist(d.trace.length - 6)
+                                : d.trace;
+                            final mono = TextStyle(
+                                fontFamily: 'monospace',
+                                fontSize: 11,
+                                color: cs.onInverseSurface);
+                            final monoFaint = mono.copyWith(
+                                fontSize: 10,
+                                color:
+                                    cs.onInverseSurface.withValues(alpha: 0.75));
+                            return Column(
+                              crossAxisAlignment: CrossAxisAlignment.start,
+                              mainAxisSize: MainAxisSize.min,
+                              children: [
+                                Text(
+                                    _penDebug.isEmpty
+                                        ? 'hover / draw with the pen…'
+                                        : _penDebug,
+                                    style: mono),
+                                const SizedBox(height: 4),
+                                Text(d.summary(), style: mono),
+                                if (tail.isNotEmpty) ...[
+                                  const SizedBox(height: 4),
+                                  Text(tail.join('\n'), style: monoFaint),
+                                ],
+                                const SizedBox(height: 4),
+                                Text(
+                                    'log: ${DiagnosticLogger.instance.path ?? "(developer.log only)"}',
+                                    style: monoFaint),
+                                Align(
+                                  alignment: Alignment.centerRight,
+                                  child: TextButton(
+                                    onPressed: () =>
+                                        InputDiagnostics.instance.reset(),
+                                    child: Text('Reset stats',
+                                        style:
+                                            TextStyle(color: cs.inversePrimary)),
+                                  ),
+                                ),
+                              ],
+                            );
+                          },
                         ),
                       ),
                     ),
@@ -621,15 +645,17 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
             _ToolButton(
               icon: Icons.bug_report_outlined,
               selected: _showPenDebug,
-              tooltip: 'Pen + zoom diagnostic',
-              onPressed: () => setState(() {
-                _showPenDebug = !_showPenDebug;
-                if (_showPenDebug) {
-                  _zoomMin = double.infinity;
-                  _zoomMax = 0.0;
-                  _zoomNow = _transform.value.getMaxScaleOnAxis();
+              tooltip: 'Input diagnostic (writes a log file)',
+              onPressed: () {
+                final on = !_showPenDebug;
+                setState(() => _showPenDebug = on);
+                if (on) {
+                  InputDiagnostics.instance.reset();
+                  DiagnosticLogger.instance.start();
+                } else {
+                  DiagnosticLogger.instance.stop();
                 }
-              }),
+              },
             ),
           ],
         ),