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/diagnostics/badnote_log.dart

@@ -0,0 +1,164 @@
+// Global structured logging bus for BadNote.
+//
+// Always-on (unlike the old PDF-only DiagnosticLogger opt-in). Writes NDJSON
+// lines to a rotating session file under the app documents directory so a
+// Surface user can export a diagnostic pack without attaching a debugger.
+
+import 'dart:async';
+import 'dart:convert';
+import 'dart:developer' as developer;
+import 'dart:io';
+
+import 'package:path_provider/path_provider.dart';
+import 'package:uuid/uuid.dart';
+
+enum LogLevel { trace, debug, info, warn, error }
+
+/// Known subsystems — keep the set small so filters stay useful.
+abstract final class LogSubsystem {
+  static const shell = 'shell';
+  static const ink = 'ink';
+  static const arbiter = 'arbiter';
+  static const penNative = 'pen_native';
+  static const pdf = 'pdf';
+  static const office = 'office';
+  static const board = 'board';
+  static const sync = 'sync';
+  static const diag = 'diag';
+  static const frame = 'frame';
+}
+
+class BadNoteLog {
+  BadNoteLog._();
+  static final BadNoteLog instance = BadNoteLog._();
+
+  final String sessionId = const Uuid().v4();
+  final List<Map<String, Object?>> _ring = <Map<String, Object?>>[];
+  static const int _ringCap = 4000;
+
+  File? _file;
+  Directory? _dir;
+  Timer? _flushTimer;
+  final List<String> _pending = <String>[];
+  bool _started = false;
+  LogLevel minLevel = LogLevel.debug;
+
+  /// Absolute path of the current session log, once [start] succeeds.
+  String? get path => _file?.path;
+
+  Directory? get directory => _dir;
+
+  Future<void> start() async {
+    if (_started) return;
+    _started = true;
+    try {
+      Directory base;
+      try {
+        base = await getApplicationDocumentsDirectory();
+      } catch (_) {
+        base = await getTemporaryDirectory();
+      }
+      _dir = Directory(
+        '${base.path}${Platform.pathSeparator}badnote_diagnostics',
+      );
+      if (!await _dir!.exists()) {
+        await _dir!.create(recursive: true);
+      }
+      final stamp = DateTime.now()
+          .toIso8601String()
+          .replaceAll(':', '-')
+          .replaceAll('.', '-');
+      _file = File(
+        '${_dir!.path}${Platform.pathSeparator}session_$stamp.ndjson',
+      );
+      await _file!.writeAsString(
+        '${jsonEncode({
+          'ts': DateTime.now().toIso8601String(),
+          'level': 'info',
+          'subsystem': LogSubsystem.diag,
+          'msg': 'session_start',
+          'sessionId': sessionId,
+          'platform': Platform.operatingSystem,
+          'osVersion': Platform.operatingSystemVersion,
+        })}\n',
+        flush: true,
+      );
+      _flushTimer = Timer.periodic(const Duration(seconds: 1), (_) => _flush());
+      info(LogSubsystem.diag, 'log file ready', fields: {'path': _file!.path});
+    } catch (e) {
+      // Logging must never crash the app.
+      developer.log('BadNoteLog start failed: $e', name: 'badnote');
+    }
+  }
+
+  void trace(String subsystem, String msg, {Map<String, Object?>? fields}) =>
+      _emit(LogLevel.trace, subsystem, msg, fields);
+
+  void debug(String subsystem, String msg, {Map<String, Object?>? fields}) =>
+      _emit(LogLevel.debug, subsystem, msg, fields);
+
+  void info(String subsystem, String msg, {Map<String, Object?>? fields}) =>
+      _emit(LogLevel.info, subsystem, msg, fields);
+
+  void warn(String subsystem, String msg, {Map<String, Object?>? fields}) =>
+      _emit(LogLevel.warn, subsystem, msg, fields);
+
+  void error(String subsystem, String msg, {Map<String, Object?>? fields}) =>
+      _emit(LogLevel.error, subsystem, msg, fields);
+
+  void _emit(
+    LogLevel level,
+    String subsystem,
+    String msg,
+    Map<String, Object?>? fields,
+  ) {
+    if (level.index < minLevel.index) return;
+    final entry = <String, Object?>{
+      'ts': DateTime.now().toIso8601String(),
+      'level': level.name,
+      'subsystem': subsystem,
+      'msg': msg,
+      'sessionId': sessionId,
+      if (fields != null) ...fields,
+    };
+    _ring.add(entry);
+    if (_ring.length > _ringCap) {
+      _ring.removeRange(0, _ring.length - _ringCap);
+    }
+    final line = jsonEncode(entry);
+    developer.log(line, name: 'badnote.$subsystem');
+    if (_file != null) {
+      _pending.add(line);
+      if (_pending.length >= 200) {
+        unawaited(_flush());
+      }
+    }
+  }
+
+  Future<void> _flush() async {
+    final file = _file;
+    if (file == null || _pending.isEmpty) return;
+    final chunk = '${_pending.join('\n')}\n';
+    _pending.clear();
+    try {
+      await file.writeAsString(chunk, mode: FileMode.append, flush: true);
+    } catch (_) {}
+  }
+
+  /// Snapshot of the in-memory ring (newest last).
+  List<Map<String, Object?>> snapshotRing() =>
+      List<Map<String, Object?>>.unmodifiable(_ring);
+
+  Future<void> flush() => _flush();
+
+  Future<void> stop() async {
+    _flushTimer?.cancel();
+    _flushTimer = null;
+    await _flush();
+  }
+}
+
+/// Bridge for legacy call sites that still use plain strings.
+void logLegacyInputLine(String line) {
+  BadNoteLog.instance.debug(LogSubsystem.penNative, line);
+}