feat: unified shell, diagnostics pack, native Office, sticky board

Make Surface remote debugging and classroom workflows viable: always-on
structured logs with one-click zip export, a single AppShell chrome,
OOXML PPTX/DOCX annotation without LibreOffice, and a first-class sticky
board. Also drop spike/legacy ink widgets and tighten pen feel
(predictor, PenInfoHistory, page-tile layer).

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/editor/canvas/pen_canvas.dart

@@ -25,11 +25,13 @@ import '../engine/brush.dart';
 import '../engine/stroke_eraser.dart';
 import '../engine/stroke_geometry.dart' show kDefaultPenThinning;
 import '../engine/stroke_model.dart';
+import '../engine/stroke_predictor.dart';
 import '../engine/stroke_store.dart';
 import '../input/input_arbiter.dart' as arbiter;
 import '../input/pen_config.dart';
 import '../input/pressure_curve.dart';
 import '../input/pen_input_service.dart';
+import '../../diagnostics/pen_event_ring.dart';
 import '../engine/shape_geometry.dart';
 import '../render/ink_picture_cache.dart';
 import '../render/live_ink_painter.dart' as render;
@@ -210,6 +212,9 @@ class _PenCanvasState extends State<PenCanvas> {
 
   /// In-progress stroke points (normalized).
   final List<PenPoint> _livePoints = [];
+  final StrokePredictor _predictor = StrokePredictor();
+  /// Count of real (non-predicted) points in [_livePoints].
+  int _realPointCount = 0;
 
   /// Live stroke snapshot handed to the LiveInkPainter; null when idle.
   PenStroke? _liveStroke;
@@ -407,12 +412,21 @@ class _PenCanvasState extends State<PenCanvas> {
   /// Decide whether the gesture currently forming should DRAW. Delegates to the
   /// pure [arbiter.shouldDraw] (unit-tested truth table) so the live canvas and
   /// the tests can never disagree on the rule.
-  bool _shouldDraw(PointerDeviceKind kind) => arbiter.shouldDraw(
-        activePointerCount: _activePointers.length,
-        kind: kind,
-        fingerDrawingEnabled: _fingerDrawingEnabled,
-        hwPanActive: _hwPanActive,
-      );
+  bool _shouldDraw(PointerDeviceKind kind) {
+    final draw = arbiter.shouldDraw(
+      activePointerCount: _activePointers.length,
+      kind: kind,
+      fingerDrawingEnabled: _fingerDrawingEnabled,
+      hwPanActive: _hwPanActive,
+    );
+    PenEventRing.instance.recordArbiter(
+      activeCount: _activePointers.length,
+      deviceKind: kind.name,
+      draw: draw,
+      fingerDrawing: _fingerDrawingEnabled,
+    );
+    return draw;
+  }
 
   // --- Coordinate mapping ---------------------------------------------------
 
@@ -437,6 +451,8 @@ class _PenCanvasState extends State<PenCanvas> {
   void _startStroke(PointerDownEvent event) {
     _drawPointer = event.pointer;
     _livePoints.clear();
+    _realPointCount = 0;
+    _predictor.reset();
     _shapeStart = null;
     _selectLast = null;
     _selectDragging = false;
@@ -469,7 +485,10 @@ class _PenCanvasState extends State<PenCanvas> {
       return;
     }
 
-    if (p != null) _livePoints.add(p);
+    if (p != null) {
+      _livePoints.add(p);
+      _realPointCount = _livePoints.length;
+    }
     _updateLiveStroke();
   }
 
@@ -507,7 +526,21 @@ class _PenCanvasState extends State<PenCanvas> {
       return;
     }
 
+    // Drop previous predicted tip before appending the real sample.
+    if (_livePoints.length > _realPointCount) {
+      _livePoints.removeRange(_realPointCount, _livePoints.length);
+    }
     _livePoints.add(p);
+    _realPointCount = _livePoints.length;
+    final pred = _predictor.observe(Offset(p.x, p.y), p.pressure ?? 0.5);
+    if (pred != null) {
+      _livePoints.add(PenPoint(
+        pred.offset.dx.clamp(0.0, 1.0),
+        pred.offset.dy.clamp(0.0, 1.0),
+        pred.pressure,
+        tilt: p.tilt,
+      ));
+    }
     _updateLiveStroke();
   }
 
@@ -533,6 +566,10 @@ class _PenCanvasState extends State<PenCanvas> {
     } else if (tool == CanvasTool.select) {
       // Nothing to commit on release: selection + moves were applied live.
     } else if (!wasEraser && _livePoints.isNotEmpty) {
+      // Never commit predicted tips — only real digitizer samples.
+      if (_livePoints.length > _realPointCount) {
+        _livePoints.removeRange(_realPointCount, _livePoints.length);
+      }
       widget.onStrokeComplete(
         PenStroke(
           points: List.of(_livePoints),
@@ -548,6 +585,8 @@ class _PenCanvasState extends State<PenCanvas> {
     _selectLast = null;
     _selectDragging = false;
     _livePoints.clear();
+    _realPointCount = 0;
+    _predictor.reset();
     _eraserCursor.value = null; // hide the preview when the pen lifts
     setState(() => _liveStroke = null);
   }