Timeline: exposes simple request for backward pagination

libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/timeline/AsyncMatrixTimeline.kt

@@ -77,6 +77,10 @@ class AsyncMatrixTimeline(
     override val paginationState: StateFlow<MatrixTimeline.PaginationState> = _paginationState
     override val timelineItems: Flow<List<MatrixTimelineItem>> = _timelineItems
 
+    override suspend fun paginateBackwards(requestSize: Int): Result<Unit> {
+        return timeline.await().paginateBackwards(requestSize)
+    }
+
     override suspend fun paginateBackwards(requestSize: Int, untilNumberOfItems: Int): Result<Unit> {
         return timeline.await().paginateBackwards(requestSize, untilNumberOfItems)
     }

libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/timeline/RustMatrixTimeline.kt

@@ -188,6 +188,14 @@ class RustMatrixTimeline(
         }
     }
 
+    override suspend fun paginateBackwards(requestSize: Int): Result<Unit> {
+        val paginationOptions = PaginationOptions.SimpleRequest(
+            eventLimit = requestSize.toUShort(),
+            waitForToken = true,
+        )
+        return paginateBackwards(paginationOptions)
+    }
+
     override suspend fun paginateBackwards(requestSize: Int, untilNumberOfItems: Int): Result<Unit> {
         val paginationOptions = PaginationOptions.UntilNumItems(
             eventLimit = requestSize.toUShort(),
@@ -198,6 +206,7 @@ class RustMatrixTimeline(
     }
 
     private suspend fun paginateBackwards(paginationOptions: PaginationOptions): Result<Unit> = withContext(dispatcher) {
+        initLatch.await()
         runCatching {
             if (!canBackPaginate()) throw TimelineException.CannotPaginate
             Timber.v("Start back paginating for room ${matrixRoom.roomId} ")