fix: coalesce pinch updates and stop live zoom write-back

Surface Aug6 diag showed sDrop=0 but ~220 same-ms dual ZOOM frames and √2 cur ping-pong from reading currentZoom back into pinch state. Flush once per microtask and embed gitSha in diagnostic meta.

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

lib/diagnostics/diagnostic_export.dart

@@ -1,5 +1,6 @@
 // Build a zip diagnostic pack the user can hand back for remote debugging.
 
+import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
@@ -13,6 +14,18 @@ import 'badnote_log.dart';
 import 'frame_sampler.dart';
 import 'pen_event_ring.dart';
 
+/// Injected at build/export time so Surface packages can be matched to git.
+/// Override via `--dart-define=BADNOTE_GIT_SHA=...` in CI.
+const String kBadNoteGitSha = String.fromEnvironment(
+  'BADNOTE_GIT_SHA',
+  defaultValue: 'dev',
+);
+
+const String kBadNoteBuildTime = String.fromEnvironment(
+  'BADNOTE_BUILD_TIME',
+  defaultValue: '',
+);
+
 class DiagnosticExportResult {
   DiagnosticExportResult({required this.zipPath, required this.bytes});
 
@@ -34,6 +47,8 @@ class DiagnosticExport {
     final meta = <String, Object?>{
       'exportedAt': DateTime.now().toIso8601String(),
       'sessionId': log.sessionId,
+      'gitSha': kBadNoteGitSha,
+      'buildTime': kBadNoteBuildTime.isEmpty ? null : kBadNoteBuildTime,
       'platform': Platform.operatingSystem,
       'osVersion': Platform.operatingSystemVersion,
       'localHostname': Platform.localHostname,
@@ -48,7 +63,8 @@ class DiagnosticExport {
       'zoom': InputDiagnostics.instance.summary(),
       'frames': FrameSampler.instance.summary(),
       'instructions':
-          'Reproduce the issue for ~3 minutes with diagnostics on, then share this zip.',
+          'Reproduce the issue for ~3 minutes with diagnostics on, then share this zip. '
+          'Confirm meta.gitSha matches the CI commit you installed.',
     };
 
     final archive = Archive();