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/input_diagnostics.dart

@@ -0,0 +1,90 @@
+// lib/editor/canvas/input_diagnostics.dart
+//
+// Live zoom/pan diagnostics for the pen canvas. PenInteractiveViewer records one
+// entry per scale-update frame; the editor's diagnostic overlay displays the
+// accumulated summary + a rolling trace so a SINGLE device session reveals the
+// nature of any "跳变" (is it a raw-scale spike, a focal/position jump, or a
+// pointer-count oscillation?). All numbers reset via [reset].
+
+import 'package:flutter/foundation.dart';
+
+import '../input/diagnostic_logger.dart';
+
+class InputDiagnostics extends ChangeNotifier {
+  InputDiagnostics._();
+  static final InputDiagnostics instance = InputDiagnostics._();
+
+  int frames = 0;
+  int scaleDropped = 0; // frames rejected as a scale glitch
+  int focalDropped = 0; // frames rejected as a focal/position glitch
+  int rebaselines = 0; // pointer-count re-baselines
+  int pointerCountMax = 0;
+  double rawScaleMin = double.infinity, rawScaleMax = 0;
+  double scaleMin = double.infinity, scaleMax = 0;
+  double maxFocalJumpPx = 0; // largest single-frame local focal delta
+  double maxAppliedScaleJump = 1; // largest single-frame applied scale ratio
+
+  final List<String> _trace = <String>[];
+  List<String> get trace => List.unmodifiable(_trace);
+
+  void recordRebaseline() {
+    rebaselines++;
+    DiagnosticLogger.instance.log('ZOOM rebaseline');
+    notifyListeners();
+  }
+
+  void recordScaleFrame({
+    required double rawScale,
+    required int pointerCount,
+    required double currentScale,
+    required double appliedChange, // 1.0 when the frame was dropped
+    required double focalJumpPx,
+    required bool scaleDrop,
+    required bool focalDrop,
+  }) {
+    frames++;
+    if (scaleDrop) scaleDropped++;
+    if (focalDrop) focalDropped++;
+    if (rawScale < rawScaleMin) rawScaleMin = rawScale;
+    if (rawScale > rawScaleMax) rawScaleMax = rawScale;
+    final double resulting = currentScale * appliedChange;
+    if (resulting < scaleMin) scaleMin = resulting;
+    if (resulting > scaleMax) scaleMax = resulting;
+    if (pointerCount > pointerCountMax) pointerCountMax = pointerCount;
+    if (focalJumpPx > maxFocalJumpPx) maxFocalJumpPx = focalJumpPx;
+    final double jump = appliedChange >= 1 ? appliedChange : 1 / appliedChange;
+    if (jump > maxAppliedScaleJump) maxAppliedScaleJump = jump;
+
+    final String line = 'p$pointerCount raw=${rawScale.toStringAsFixed(3)} '
+        'ch=${appliedChange.toStringAsFixed(3)} '
+        'cur=${currentScale.toStringAsFixed(3)} '
+        'fj=${focalJumpPx.toStringAsFixed(0)}'
+        '${scaleDrop ? " SDROP" : ""}${focalDrop ? " FDROP" : ""}';
+    _trace.add(line);
+    if (_trace.length > 24) _trace.removeAt(0);
+    DiagnosticLogger.instance.log('ZOOM $line');
+    notifyListeners();
+  }
+
+  void reset() {
+    frames = scaleDropped = focalDropped = rebaselines = pointerCountMax = 0;
+    rawScaleMin = scaleMin = double.infinity;
+    rawScaleMax = scaleMax = 0;
+    maxFocalJumpPx = 0;
+    maxAppliedScaleJump = 1;
+    _trace.clear();
+    notifyListeners();
+  }
+
+  String _f(double v) => v.isFinite ? v.toStringAsFixed(2) : '-';
+
+  String summary() {
+    if (frames == 0) return 'zoom: (pinch to record)';
+    return 'zoom f=$frames sDrop=$scaleDropped fDrop=$focalDropped '
+        'rebase=$rebaselines pMax=$pointerCountMax\n'
+        '  raw=${_f(rawScaleMin)}..${_f(rawScaleMax)} '
+        'scale=${_f(scaleMin)}..${_f(scaleMax)}\n'
+        '  maxFocalJump=${maxFocalJumpPx.toStringAsFixed(0)}px '
+        'maxScaleJump=${_f(maxAppliedScaleJump)}';
+  }
+}

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();
                 }
-              }),
+              },
             ),
           ],
         ),

lib/editor/canvas/pen_interactive_viewer.dart

@@ -31,6 +31,8 @@ import 'package:flutter/gestures.dart';
 import 'package:flutter/physics.dart';
 import 'package:flutter/widgets.dart';
 
+import 'input_diagnostics.dart';
+
 /// Devices allowed to pan/zoom. Stylus + invertedStylus are excluded so the pen
 /// is owned exclusively by the drawing `Listener`.
 const Set<PointerDeviceKind> _kPanZoomDevices = <PointerDeviceKind>{
@@ -46,6 +48,11 @@ const Set<PointerDeviceKind> _kPanZoomDevices = <PointerDeviceKind>{
 const double _kScaleGlitchHi = 1.4;
 const double _kScaleGlitchLo = 1 / _kScaleGlitchHi;
 
+/// During a 2-finger gesture the focal point (finger midpoint) should move
+/// smoothly. A single-frame local jump beyond this is a Windows touch misread,
+/// and the frame is dropped (position-jump guard).
+const double _kFocalGlitchPx = 250.0;
+
 const double _kDrag = 0.0000135;
 
 enum _GestureType { pan, scale }
@@ -162,9 +169,11 @@ class _PenInteractiveViewerState extends State<PenInteractiveViewer>
       _lastPointerCount = details.pointerCount;
       _scaleStart = _transformer.value.getMaxScaleOnAxis();
       _referenceFocalPoint = _transformer.toScene(details.localFocalPoint);
+      InputDiagnostics.instance.recordRebaseline();
       return;
     }
 
+    final double focalJumpPx = details.focalPointDelta.distance;
     final Offset focalPointScene = _transformer.toScene(details.localFocalPoint);
 
     if (_gestureType == _GestureType.pan) {
@@ -175,16 +184,36 @@ class _PenInteractiveViewerState extends State<PenInteractiveViewer>
     }
     if (!_gestureIsSupported(_gestureType)) return;
 
+    // Position-jump guard: during a pinch the focal midpoint should move
+    // smoothly; a big single-frame jump is a touch misread → drop the frame.
+    final bool focalDrop =
+        details.pointerCount >= 2 && focalJumpPx > _kFocalGlitchPx;
+
+    void record(double appliedChange, bool scaleDrop, bool focalDropped) {
+      InputDiagnostics.instance.recordScaleFrame(
+        rawScale: details.scale,
+        pointerCount: details.pointerCount,
+        currentScale: scale,
+        appliedChange: appliedChange,
+        focalJumpPx: focalJumpPx,
+        scaleDrop: scaleDrop,
+        focalDrop: focalDropped,
+      );
+    }
+
     switch (_gestureType!) {
       case _GestureType.scale:
         assert(_scaleStart != null);
         final double desiredScale = _scaleStart! * details.scale;
         final double scaleChange = desiredScale / scale;
-        // Glitch rejection: drop a frame that demands an implausible per-frame
-        // scale jump (a Windows multi-touch position glitch). The next good
-        // frame resumes from the true finger positions, so the spike never
-        // shows — unlike clamping, which still applied a visible partial jump.
-        if (scaleChange > _kScaleGlitchHi || scaleChange < _kScaleGlitchLo) {
+        // Drop a frame demanding an implausible per-frame scale jump (Windows
+        // multi-touch glitch) OR an implausible focal jump. Absolute tracking
+        // means the next good frame resumes from the true finger positions, so
+        // the spike never shows.
+        final bool scaleDrop =
+            scaleChange > _kScaleGlitchHi || scaleChange < _kScaleGlitchLo;
+        if (scaleDrop || focalDrop) {
+          record(1.0, scaleDrop, focalDrop);
           return;
         }
         _transformer.value = _matrixScale(_transformer.value, scaleChange);
@@ -203,16 +232,23 @@ class _PenInteractiveViewerState extends State<PenInteractiveViewer>
         if (_round(_referenceFocalPoint!) != _round(focalPointSceneCheck)) {
           _referenceFocalPoint = focalPointSceneCheck;
         }
+        record(scaleChange, false, false);
 
       case _GestureType.pan:
         assert(_referenceFocalPoint != null);
         // Throw away near-scale frames so a stale reference can't jump the pan.
         if (details.scale != 1.0) return;
+        if (focalDrop) {
+          _referenceFocalPoint = _transformer.toScene(details.localFocalPoint);
+          record(1.0, false, true);
+          return;
+        }
         final Offset translationChange =
             focalPointScene - _referenceFocalPoint!;
         _transformer.value =
             _matrixTranslate(_transformer.value, translationChange);
         _referenceFocalPoint = _transformer.toScene(details.localFocalPoint);
+        record(1.0, false, false);
     }
   }
 

lib/editor/input/diagnostic_logger.dart

@@ -0,0 +1,90 @@
+// lib/editor/input/diagnostic_logger.dart
+//
+// On-device input diagnostics. When the user manually enables the diagnostic
+// (the toolbar toggle), every native pen event (raw button/flag/tilt fields)
+// and every zoom frame is emitted through the standard `dart:developer` log
+// channel (name 'badnote.input') — capturable via `flutter run`, DevTools, or
+// any log tool — AND mirrored to a text file as a fallback for the packaged
+// GUI build, which has no attached console. Disabled by default (no overhead).
+
+import 'dart:async';
+import 'dart:developer' as developer;
+import 'dart:io';
+
+import 'package:path_provider/path_provider.dart';
+
+class DiagnosticLogger {
+  DiagnosticLogger._();
+  static final DiagnosticLogger instance = DiagnosticLogger._();
+
+  final List<String> _buffer = <String>[];
+  File? _file;
+  Timer? _timer;
+  int _epochMs = 0;
+
+  bool _active = false;
+  bool get isActive => _active;
+
+  /// Absolute path of the current log file (shown in the overlay), or null.
+  String? path;
+
+  /// Begin a session. Enables the `dart:developer` log channel immediately and
+  /// opens the fallback file (best-effort). Safe to call repeatedly.
+  Future<void> start() async {
+    if (_active) return;
+    _active = true; // developer.log works even if the file can't be opened
+    _epochMs = DateTime.now().millisecondsSinceEpoch;
+    developer.log('--- session start ${DateTime.now().toIso8601String()} ---',
+        name: 'badnote.input');
+    try {
+      Directory dir;
+      try {
+        dir = await getApplicationDocumentsDirectory();
+      } catch (_) {
+        dir = await getTemporaryDirectory();
+      }
+      final file = File('${dir.path}${Platform.pathSeparator}badnote_input_log.txt');
+      await file.writeAsString(
+        '# BadNote input diagnostic log\n'
+        '# started ${DateTime.now().toIso8601String()}\n'
+        '# columns: <ms> <kind> <fields...>\n',
+        flush: true,
+      );
+      _file = file;
+      path = file.path;
+      _buffer.clear();
+      _timer = Timer.periodic(const Duration(seconds: 1), (_) => _flush());
+    } catch (_) {
+      // File is a fallback; never break the app over it.
+    }
+  }
+
+  /// Emit one diagnostic line through the standard log channel and the file.
+  void log(String line) {
+    if (!_active) return;
+    developer.log(line, name: 'badnote.input');
+    if (_file == null) return;
+    final t = DateTime.now().millisecondsSinceEpoch - _epochMs;
+    _buffer.add('$t $line');
+    if (_buffer.length >= 1000) _flush();
+  }
+
+  Future<void> _flush() async {
+    final file = _file;
+    if (file == null || _buffer.isEmpty) return;
+    final chunk = '${_buffer.join('\n')}\n';
+    _buffer.clear();
+    try {
+      await file.writeAsString(chunk, mode: FileMode.append, flush: true);
+    } catch (_) {}
+  }
+
+  /// Flush and stop. The file remains on disk for retrieval.
+  Future<void> stop() async {
+    if (!_active) return;
+    _active = false;
+    _timer?.cancel();
+    _timer = null;
+    await _flush();
+  }
+}

lib/editor/input/pen_input_service.dart

@@ -23,6 +23,8 @@ import 'dart:async';
 
 import 'package:flutter/services.dart';
 
+import 'diagnostic_logger.dart';
+
 /// Latest hardware pen state delivered by the native observer.
 class PenHardwareState {
   const PenHardwareState({
@@ -94,17 +96,27 @@ class PenInputService {
   bool get isActive => _active;
   bool _active = false;
 
-  // Native-side diagnostics (see windows/runner/pen_channel.cpp): how many
-  // WM_POINTER / PT_PEN / legacy-mouse messages the observer has seen. Lets the
-  // on-device overlay tell us WHICH layer is failing for buttons/tilt.
+  // Native-side diagnostics (see windows/runner/pen_channel.cpp).
   int _diagPtr = 0;
   int _diagPen = 0;
   int _diagMouse = 0;
   int _diagMsg = 0;
+  int _orPtrFlags = 0;
+  int _orPenFlags = 0;
+  int _orPenMask = 0;
+  int _btnChangeLast = 0;
+  int _tiltAbsMax = 0;
 
-  /// One-line native readout for the diagnostic overlay.
+  String _hex(int v) => '0x${v.toRadixString(16)}';
+
+  /// Multi-line native readout for the diagnostic overlay. The OR-accumulated
+  /// flag fields are the ground truth for which field carries the side/eraser
+  /// button: e.g. orPtrFlags with bit 0x20 (POINTER_FLAG_SECONDBUTTON) set means
+  /// the barrel button IS detectable.
   String get debugSummary => _active
-      ? 'native ptr=$_diagPtr pen=$_diagPen mouse=$_diagMouse msg=0x${_diagMsg.toRadixString(16)}'
+      ? 'native ptr=$_diagPtr pen=$_diagPen mouse=$_diagMouse msg=${_hex(_diagMsg)}'
+          '\n  orPtrFlags=${_hex(_orPtrFlags)} orPenFlags=${_hex(_orPenFlags)}'
+          ' mask=${_hex(_orPenMask)} btnChg=$_btnChangeLast tiltMax=$_tiltAbsMax'
       : 'native: channel silent (no events)';
 
   /// Begins listening to the native channel. Idempotent; safe on any platform
@@ -140,9 +152,35 @@ class PenInputService {
     _diagPen = (event['diagPen'] as num?)?.toInt() ?? _diagPen;
     _diagMouse = (event['diagMouse'] as num?)?.toInt() ?? _diagMouse;
     _diagMsg = (event['diagMsg'] as num?)?.toInt() ?? _diagMsg;
+    _orPtrFlags = (event['orPtrFlags'] as num?)?.toInt() ?? _orPtrFlags;
+    _orPenFlags = (event['orPenFlags'] as num?)?.toInt() ?? _orPenFlags;
+    _orPenMask = (event['orPenMask'] as num?)?.toInt() ?? _orPenMask;
+    _btnChangeLast = (event['btnChangeLast'] as num?)?.toInt() ?? _btnChangeLast;
+    _tiltAbsMax = (event['tiltAbsMax'] as num?)?.toInt() ?? _tiltAbsMax;
     _active = true;
+
+    // Log a PEN line whenever the raw per-event button/flag fields change, so
+    // the file captures exactly which field a button press sets (without
+    // flooding on every high-rate WM_POINTERUPDATE).
+    final rawPtr = (event['rawPtrFlags'] as num?)?.toInt() ?? 0;
+    final rawPen = (event['rawPenFlags'] as num?)?.toInt() ?? 0;
+    final rawMask = (event['rawPenMask'] as num?)?.toInt() ?? 0;
+    final btnChange = (event['btnChange'] as num?)?.toInt() ?? 0;
+    final key = '$rawPtr,$rawPen,$rawMask,$btnChange,${_current.tiltX},${_current.tiltY}';
+    if (key != _lastPenLogKey) {
+      _lastPenLogKey = key;
+      DiagnosticLogger.instance.log(
+        'PEN ptrFlags=0x${rawPtr.toRadixString(16)} '
+        'penFlags=0x${rawPen.toRadixString(16)} '
+        'mask=0x${rawMask.toRadixString(16)} btnChg=$btnChange '
+        'tilt=${_current.tiltX.toStringAsFixed(0)},${_current.tiltY.toStringAsFixed(0)} '
+        'msg=0x${_diagMsg.toRadixString(16)} resolved=0x${flags.toRadixString(16)}',
+      );
+    }
   }
 
+  String _lastPenLogKey = '';
+
   /// Stops listening and resets state.
   void stop() {
     _sub?.cancel();

windows/runner/pen_channel.cpp

@@ -23,6 +23,15 @@ int g_pen_msgs = 0;
 int g_mouse_msgs = 0;
 int g_last_msg = 0;
 
+// OR-accumulated raw flag fields, so a momentary button press is CAPTURED and
+// held (a live readout would miss it). These are the ground truth for "which
+// field/bit does the side button / eraser set?".
+int g_ptr_flags_or = 0;   // POINTER_INFO.pointerFlags  (POINTER_FLAG_SECONDBUTTON = barrel on many pens)
+int g_pen_flags_or = 0;   // POINTER_PEN_INFO.penFlags   (PEN_FLAG_BARREL/INVERTED/ERASER)
+int g_pen_mask_or = 0;    // POINTER_PEN_INFO.penMask
+int g_btn_change_last = 0; // last non-zero POINTER_INFO.ButtonChangeType
+int g_tilt_abs_max = 0;   // max |tiltX|,|tiltY| seen
+
 }  // namespace
 
 void RegisterPenChannel(flutter::FlutterEngine* engine) {
@@ -76,6 +85,10 @@ void ObservePenMessage(UINT message, WPARAM wparam, LPARAM lparam) {
   int flags = 0;
   double tilt_x = 0.0;
   double tilt_y = 0.0;
+  int raw_ptr_flags = 0;
+  int raw_pen_flags = 0;
+  int raw_pen_mask = 0;
+  int btn_change = 0;
 
   if (is_pointer) {
     ++g_ptr_msgs;
@@ -85,11 +98,32 @@ void ObservePenMessage(UINT message, WPARAM wparam, LPARAM lparam) {
       POINTER_PEN_INFO ppi{};
       if (GetPointerPenInfo(pointerId, &ppi)) {
         ++g_pen_msgs;
-        if (ppi.penFlags & PEN_FLAG_BARREL)   flags |= 1;
-        if (ppi.penFlags & PEN_FLAG_INVERTED) flags |= 2;
-        if (ppi.penFlags & PEN_FLAG_ERASER)   flags |= 4;
+        raw_pen_flags = static_cast<int>(ppi.penFlags);
+        raw_pen_mask = static_cast<int>(ppi.penMask);
+        raw_ptr_flags = static_cast<int>(ppi.pointerInfo.pointerFlags);
+        btn_change = static_cast<int>(ppi.pointerInfo.ButtonChangeType);
         tilt_x = static_cast<double>(ppi.tiltX);
         tilt_y = static_cast<double>(ppi.tiltY);
+
+        // Barrel/side button can arrive in EITHER penFlags (PEN_FLAG_BARREL) or
+        // pointerFlags (POINTER_FLAG_SECONDBUTTON) depending on the pen/driver,
+        // so check both. Eraser end = inverted/eraser pen flags.
+        const bool barrel = (ppi.penFlags & PEN_FLAG_BARREL) ||
+                            (ppi.pointerInfo.pointerFlags & POINTER_FLAG_SECONDBUTTON);
+        const bool inverted = (ppi.penFlags & PEN_FLAG_INVERTED) != 0;
+        const bool eraser = (ppi.penFlags & PEN_FLAG_ERASER) != 0;
+        if (barrel)   flags |= 1;
+        if (inverted) flags |= 2;
+        if (eraser)   flags |= 4;
+
+        g_ptr_flags_or |= raw_ptr_flags;
+        g_pen_flags_or |= raw_pen_flags;
+        g_pen_mask_or |= raw_pen_mask;
+        if (btn_change != 0) g_btn_change_last = btn_change;
+        const int ax = ppi.tiltX < 0 ? -ppi.tiltX : ppi.tiltX;
+        const int ay = ppi.tiltY < 0 ? -ppi.tiltY : ppi.tiltY;
+        if (ax > g_tilt_abs_max) g_tilt_abs_max = ax;
+        if (ay > g_tilt_abs_max) g_tilt_abs_max = ay;
       }
     }
     if (message == WM_POINTERUP) {
@@ -97,8 +131,9 @@ void ObservePenMessage(UINT message, WPARAM wparam, LPARAM lparam) {
     }
   }
 
-  // Always emit the diagnostic counters so the Dart overlay can show whether
-  // WM_POINTER / PT_PEN ever reach this observer.
+  // Emit the resolved flags/tilt PLUS the full raw + OR-accumulated diagnostic
+  // set, so a single device session reveals exactly which field carries the
+  // button and what tilt/mask the pen reports.
   flutter::EncodableMap payload{
       {flutter::EncodableValue("flags"), flutter::EncodableValue(flags)},
       {flutter::EncodableValue("tiltX"), flutter::EncodableValue(tilt_x)},
@@ -107,6 +142,15 @@ void ObservePenMessage(UINT message, WPARAM wparam, LPARAM lparam) {
       {flutter::EncodableValue("diagPen"), flutter::EncodableValue(g_pen_msgs)},
       {flutter::EncodableValue("diagMouse"), flutter::EncodableValue(g_mouse_msgs)},
       {flutter::EncodableValue("diagMsg"), flutter::EncodableValue(g_last_msg)},
+      {flutter::EncodableValue("rawPtrFlags"), flutter::EncodableValue(raw_ptr_flags)},
+      {flutter::EncodableValue("rawPenFlags"), flutter::EncodableValue(raw_pen_flags)},
+      {flutter::EncodableValue("rawPenMask"), flutter::EncodableValue(raw_pen_mask)},
+      {flutter::EncodableValue("btnChange"), flutter::EncodableValue(btn_change)},
+      {flutter::EncodableValue("orPtrFlags"), flutter::EncodableValue(g_ptr_flags_or)},
+      {flutter::EncodableValue("orPenFlags"), flutter::EncodableValue(g_pen_flags_or)},
+      {flutter::EncodableValue("orPenMask"), flutter::EncodableValue(g_pen_mask_or)},
+      {flutter::EncodableValue("btnChangeLast"), flutter::EncodableValue(g_btn_change_last)},
+      {flutter::EncodableValue("tiltAbsMax"), flutter::EncodableValue(g_tilt_abs_max)},
   };
   g_pen_sink->Success(flutter::EncodableValue(payload));
 }