feat(event cache): add a feature toggle to enable automatic back-pagination

bindings/matrix-sdk-ffi/src/client.rs

@@ -2104,6 +2104,15 @@ impl Client {
             }
         }))))
     }
+
+    /// Whether to enable automatic backpagination under certain conditions
+    /// (e.g. when processing read receipts).
+    ///
+    /// This is an experimental feature, and might cause performance issues on
+    /// large accounts. Use with caution.
+    pub async fn enable_automatic_backpagination(&self) {
+        self.inner.event_cache().config_mut().await.experimental_auto_backpagination = true;
+    }
 }
 
 #[cfg(feature = "experimental-element-recent-emojis")]

crates/matrix-sdk/src/event_cache/mod.rs

@@ -379,6 +379,11 @@ pub struct EventCacheConfig {
 
     /// Maximum number of pinned events to load, for any room.
     pub max_pinned_events_to_load: usize,
+
+    /// Whether to automatically backpaginate a room under certain conditions.
+    ///
+    /// Off by default.
+    pub experimental_auto_backpagination: bool,
 }
 
 impl EventCacheConfig {
@@ -395,6 +400,7 @@ impl Default for EventCacheConfig {
         Self {
             max_pinned_events_concurrent_requests: Self::DEFAULT_MAX_CONCURRENT_REQUESTS,
             max_pinned_events_to_load: Self::DEFAULT_MAX_EVENTS_TO_LOAD,
+            experimental_auto_backpagination: false,
         }
     }
 }