diff --git a/lib/services/field_test/field_test_export_service.dart b/lib/services/field_test/field_test_export_service.dart
index eea9ca6..0763262 100644
--- a/lib/services/field_test/field_test_export_service.dart
+++ b/lib/services/field_test/field_test_export_service.dart
@@ -57,7 +57,7 @@ class FieldTestExportService {
   }
 
   /// Step 15: Complete JSON Forensic Session Export with Versioning Identity
-  Future<String> generateFieldTestSessionJson(int rideId) async {
+  Future<String> generateFieldTestSessionJson(int rideId, {DateTime? generatedAt}) async {
     final ride = await (_db.select(_db.rides)..where((r) => r.id.equals(rideId))).getSingleOrNull();
     final summaryRecord = await (_db.select(_db.fieldTestSummaries)..where((s) => s.rideId.equals(rideId))).getSingleOrNull();
     final events = await (_db.select(_db.fieldTestEvents)
@@ -70,7 +70,7 @@ class FieldTestExportService {
 
     final Map<String, dynamic> exportMap = {
       'exportVersion': '1.0.0',
-      'generatedAt': DateTime.now().toIso8601String(),
+      'generatedAt': (generatedAt ?? DateTime.now()).toIso8601String(),
       'software': appIdentity.toJson(),
       'rideMetadata': {
         'id': ride?.id,
diff --git a/lib/services/sync/sync_bundle_worker.dart b/lib/services/sync/sync_bundle_worker.dart
index 9a9633c..0f63fa5 100644
--- a/lib/services/sync/sync_bundle_worker.dart
+++ b/lib/services/sync/sync_bundle_worker.dart
@@ -19,7 +19,8 @@ Uint8List compressFilesToZipIsolate(Map<String, String> filesMap) {
     archive.addFile(ArchiveFile(entry.key, bytes.length, bytes));
   }
   final zipEncoder = ZipEncoder();
-  final compressed = zipEncoder.encode(archive);
+  // Keep retry bytes and the recorded SHA-256 stable for unchanged ride data.
+  final compressed = zipEncoder.encode(archive, modified: DateTime.utc(1980, 1, 1));
   return Uint8List.fromList(compressed);
 }
 
@@ -41,7 +42,10 @@ class SyncBundleWorker {
       final exportService = ExportService(_db);
 
       // 1. Query local authoritative data on the main isolate
-      final sessionJson = await fieldTestExport.generateFieldTestSessionJson(rideId);
+      final sessionJson = await fieldTestExport.generateFieldTestSessionJson(
+        rideId,
+        generatedAt: ride.endTime ?? ride.startTime,
+      );
       final eventsCsv = await fieldTestExport.generateFieldTestEventsCsv(rideId);
       final telemetryCsv = await exportService.exportRideCsv(rideId);
       final gpxContent = await exportService.exportRideGpx(rideId);
diff --git a/test/r2_firestore_retry_hardening_test.dart b/test/r2_firestore_retry_hardening_test.dart
new file mode 100644
index 0000000..6a99cd1
--- /dev/null
+++ b/test/r2_firestore_retry_hardening_test.dart
@@ -0,0 +1,213 @@
+import 'dart:convert';
+import 'dart:io';
+import 'dart:typed_data';
+
+import 'package:crypto/crypto.dart';
+import 'package:drift/drift.dart' as drift;
+import 'package:drift/native.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:http/http.dart' as http;
+import 'package:http/testing.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'package:motorcycle_dash/database/database.dart';
+import 'package:motorcycle_dash/services/sync/r2_upload_service.dart';
+import 'package:motorcycle_dash/services/sync/sync_bundle_worker.dart';
+import 'package:motorcycle_dash/services/sync/sync_manager.dart';
+import 'package:motorcycle_dash/services/sync/sync_models.dart';
+import 'package:motorcycle_dash/services/sync/sync_outbox.dart';
+import 'package:motorcycle_dash/services/sync/sync_provider.dart';
+
+class _R2ThenFirestoreProvider implements SyncProvider {
+  int attempts = 0;
+  bool firestoreAvailable = false;
+  final List<String> uploadedRemoteIds = [];
+
+  @override
+  String get providerId => 'firebase';
+
+  @override
+  Future<bool> isAvailable() async => true;
+
+  @override
+  Future<bool> requiresAuthentication() async => false;
+
+  @override
+  Future<SyncResult> uploadRide(SyncItem item) async {
+    attempts++;
+    uploadedRemoteIds.add('ride_stable_123');
+    if (!firestoreAvailable) {
+      return SyncResult.temporaryFailure(
+        'Firestore unavailable after R2 upload.',
+      );
+    }
+    return SyncResult.success(remoteId: 'ride_stable_123');
+  }
+}
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  group('R2 and Firestore retry hardening', () {
+    test(
+      'retries target one deterministic R2 object, including changed bundle bytes',
+      () async {
+        final remoteIds = <String>[];
+        final objectKeys = <String>[];
+        final client = MockClient((request) async {
+          remoteIds.add(request.headers['X-Remote-Ride-Id']!);
+          final remoteRideId = request.headers['X-Remote-Ride-Id']!;
+          final objectKey = 'users/pilot_123/rides/$remoteRideId/telemetry.zip';
+          objectKeys.add(objectKey);
+          return http.Response(
+            jsonEncode({'objectKey': objectKey, 'size': 4}),
+            200,
+          );
+        });
+        final service = R2UploadService(
+          client: client,
+          workerBaseUrl: 'https://worker.test',
+        );
+
+        final first = await service.uploadTelemetryBundle(
+          idToken: 'token',
+          remoteRideId: 'ride_stable_123',
+          zipBytes: Uint8List.fromList([1, 2, 3, 4]),
+          sha256Hash: 'a' * 64,
+          appVersion: '1.0.2',
+        );
+        final retry = await service.uploadTelemetryBundle(
+          idToken: 'token',
+          remoteRideId: 'ride_stable_123',
+          zipBytes: Uint8List.fromList([4, 3, 2, 1]),
+          sha256Hash: 'b' * 64,
+          appVersion: '1.0.2',
+        );
+
+        expect(first.success, isTrue);
+        expect(retry.success, isTrue);
+        expect(remoteIds, ['ride_stable_123', 'ride_stable_123']);
+        expect(objectKeys.toSet(), hasLength(1));
+        expect(first.objectKey, retry.objectKey);
+      },
+    );
+
+    test(
+      'R2 success then Firestore failure remains durable and retries one cloud ride',
+      () async {
+        SharedPreferences.setMockInitialValues({});
+        final prefs = await SharedPreferences.getInstance();
+        final outbox = SyncOutbox(prefs);
+        final provider = _R2ThenFirestoreProvider();
+        var now = DateTime(2026, 9, 3, 12);
+        final manager = SyncManager(
+          outbox,
+          initialProviders: [provider],
+          defaultProviderId: 'firebase',
+          nowProvider: () => now,
+        );
+
+        await manager.enqueueRide(42, autoProcess: false);
+        await manager.processQueue();
+        expect(outbox.getItem(42, 'firebase')?.status, SyncStatus.retryWait);
+        expect(outbox.isRideSynced(42, 'firebase'), isFalse);
+
+        provider.firestoreAvailable = true;
+        now = now.add(const Duration(seconds: 5));
+        await manager.processQueue();
+
+        expect(outbox.getItem(42, 'firebase')?.status, SyncStatus.synced);
+        expect(provider.attempts, 2);
+        expect(provider.uploadedRemoteIds.toSet(), {'ride_stable_123'});
+        manager.dispose();
+      },
+    );
+
+    test(
+      'interrupted uploading state reloads as retryable queued work',
+      () async {
+        final item = SyncItem(
+          localRideId: 42,
+          providerId: 'firebase',
+          status: SyncStatus.uploading,
+          createdAt: DateTime(2026, 9, 3),
+        );
+        SharedPreferences.setMockInitialValues({
+          'motorsignal_sync_outbox_manifest_v2_local': jsonEncode([
+            item.toJson(),
+          ]),
+        });
+
+        final prefs = await SharedPreferences.getInstance();
+        final reloaded = SyncOutbox(prefs);
+        expect(reloaded.getItem(42, 'firebase')?.status, SyncStatus.queued);
+      },
+    );
+
+    test(
+      'completed ride bundle is byte-stable when regenerated for a retry',
+      () async {
+        final db = AppDatabase.forTesting(NativeDatabase.memory());
+        addTearDown(db.close);
+        final rideId = await db
+            .into(db.rides)
+            .insert(
+              RidesCompanion.insert(
+                startTime: DateTime(2026, 9, 3, 10),
+                endTime: drift.Value(DateTime(2026, 9, 3, 11)),
+                distanceMiles: const drift.Value(12.4),
+              ),
+            );
+        final worker = SyncBundleWorker(db);
+
+        final first = await worker.generateCompressedBundle(rideId);
+        final retry = await worker.generateCompressedBundle(rideId);
+
+        expect(first, isNotNull);
+        expect(retry, isNotNull);
+        expect(
+          sha256.convert(first!).toString(),
+          sha256.convert(retry!).toString(),
+        );
+      },
+    );
+
+    test(
+      'production path upserts one Firestore document after R2 and records its hash',
+      () {
+        final providerSource = File(
+          'lib/services/sync/firebase_sync_provider.dart',
+        ).readAsStringSync();
+        final workerSource = File(
+          'cloudflare/motorsignal-r2-worker/src/index.ts',
+        ).readAsStringSync();
+
+        expect(
+          workerSource,
+          contains(
+            r'const objectKey = `users/${authenticatedUid}/rides/${remoteRideId}/telemetry.zip`;',
+          ),
+        );
+        expect(
+          workerSource,
+          contains('await env.R2_BUCKET.put(objectKey, payloadBuffer,'),
+        );
+        expect(
+          providerSource.indexOf('uploadTelemetryBundle('),
+          lessThan(
+            providerSource.indexOf(
+              ".collection('users').doc(user.uid).collection('rides').doc(remoteRideId).set(",
+            ),
+          ),
+        );
+        expect(providerSource, contains("'sha256': sha256Hash"));
+        expect(
+          providerSource,
+          contains(
+            ".doc(remoteRideId).set(firestorePayload, SetOptions(merge: true))",
+          ),
+        );
+        expect(providerSource, contains("'telemetryBundlePath': objectKey"));
+      },
+    );
+  });
+}