fix: set prev_batch when seen in sync

lib/fake_matrix_api.dart

@@ -594,7 +594,7 @@ class FakeMatrixApi extends BaseClient {
               }
             ],
             'limited': true,
-            'prev_batch': 't34-23535_0_0',
+            'prev_batch': 't44-23535_0_0',
           },
           'ephemeral': {
             'events': [
@@ -711,7 +711,7 @@ class FakeMatrixApi extends BaseClient {
               },
             ],
             'limited': true,
-            'prev_batch': 't34-23535_0_0',
+            'prev_batch': 't34-23535_0_1',
           },
           'account_data': {
             'events': [

lib/src/client.dart

@@ -2989,7 +2989,9 @@ class Client extends MatrixApi {
           chatUpdate.unreadNotifications?.notificationCount ?? 0;
       rooms[roomIndex].highlightCount =
           chatUpdate.unreadNotifications?.highlightCount ?? 0;
-
+      if (chatUpdate.timeline?.prevBatch != null) {
+        rooms[roomIndex].prev_batch = chatUpdate.timeline?.prevBatch;
+      }
       final summary = chatUpdate.summary;
       if (summary != null) {
         final roomSummaryJson = rooms[roomIndex].summary.toJson()

test/client_test.dart

@@ -761,6 +761,31 @@ void main() {
       expect(room.lastEvent!.content['body'], '* foxies');
     });
 
+    test('set prev_batch if in sync', () async {
+      final roomId = '!726s6s6q:example.com';
+      final room = matrix.getRoomById(roomId)!;
+
+      expect(room.prev_batch, 't44-23535_0_0');
+      // put an important state event in-memory
+      await matrix.handleSync(
+        SyncUpdate.fromJson({
+          'next_batch': 'fakesync',
+          'rooms': {
+            'join': {
+              roomId: {
+                'timeline': {
+                  'events': [],
+                  'prev_batch': 'prev_batch_1',
+                },
+              },
+            },
+          },
+        }),
+      );
+
+      expect(room.prev_batch, 'prev_batch_1');
+    });
+
     test('getProfileFromUserId', () async {
       final cachedProfile = await matrix.getUserProfile('@getme:example.com');
       expect(cachedProfile.outdated, false);