store: Add comment why we can ignore unexpected TimelineSlices

crates/matrix-sdk-base/src/store/indexeddb_store.rs

@@ -525,6 +525,9 @@ impl IndexeddbStore {
                         .transpose()?;
                     if let Some(mut metadata) = metadata {
                         if !timeline.sync && Some(&timeline.start) != metadata.end.as_ref() {
+                            // This should only happen when a developer adds a wrong timeline
+                            // batch to the `StateChanges` or the server returns a wrong response
+                            // to our request.
                             warn!("Drop unexpected timeline batch for {}", room_id);
                             return Ok(());
                         }

crates/matrix-sdk-base/src/store/memory_store.rs

@@ -290,6 +290,9 @@ impl MemoryStore {
                 None
             } else if let Some(mut data) = self.room_timeline.get_mut(room) {
                 if !timeline.sync && Some(&timeline.start) != data.end.as_ref() {
+                    // This should only happen when a developer adds a wrong timeline
+                    // batch to the `StateChanges` or the server returns a wrong response
+                    // to our request.
                     warn!("Drop unexpected timeline batch for {}", room);
                     return Ok(());
                 }

crates/matrix-sdk-base/src/store/sled_store.rs

@@ -1093,6 +1093,9 @@ impl SledStore {
                     .transpose()?;
                 if let Some(mut metadata) = metadata {
                     if !timeline.sync && Some(&timeline.start) != metadata.end.as_ref() {
+                        // This should only happen when a developer adds a wrong timeline
+                        // batch to the `StateChanges` or the server returns a wrong response
+                        // to our request.
                         warn!("Drop unexpected timeline batch for {}", room_id);
                         return Ok(());
                     }