SSS: implement bump_stamp

src/api/client_server/sync/msc4186.rs

@@ -832,6 +832,17 @@ fn process_room(
             (todo_room.roomsince != 0).then(|| todo_room.roomsince.to_string())
         });
 
+    // TODO: consider only message-like PDUs here, rather than all PDUs
+    let bump_stamp = match services()
+        .rooms
+        .timeline
+        .last_timeline_count(sender_user, room_id)?
+    {
+        PduCount::Backfilled(n) | PduCount::Normal(n) => {
+            Some(UInt::new_saturating(n))
+        }
+    };
+
     let room_events: Vec<_> =
         timeline_pdus.iter().map(|(_, pdu)| pdu.to_sync_room_event()).collect();
 
@@ -1009,8 +1020,7 @@ fn process_room(
         ),
         // Count events in timeline greater than global sync counter
         num_live: None,
-        // TODO
-        bump_stamp: None,
+        bump_stamp,
         heroes,
     };
     trace!(?room, "Built room data");