Refactor state recovery after the disconnect period.

Assets/Plugins/StreamChat/Core/Configs/IStreamClientConfig.cs

@@ -36,5 +36,12 @@ public interface IStreamClientConfig
         /// Does not change server history. See <see cref="StatefulModels.IStreamChannel.MessageCacheWindow"/>.
         /// </summary>
         MessageCacheWindow DefaultMessageCacheWindow { get; set; }
+
+        /// <summary>
+        /// How the client restores local state after the websocket reconnects.
+        /// Default is <see cref="Configs.StateRecoveryStrategy.ReplayEvents"/>.
+        /// See <see cref="Configs.StateRecoveryStrategy"/> for the other options.
+        /// </summary>
+        StateRecoveryStrategy StateRecoveryStrategy { get; set; }
     }
 }

Assets/Plugins/StreamChat/Core/Configs/StateRecoveryStrategy.cs

@@ -0,0 +1,58 @@
+namespace StreamChat.Core.Configs
+{
+    /// <summary>
+    /// How <see cref="IStreamChatClient"/> restores local state after the websocket reconnects.
+    /// Set this on <see cref="IStreamClientConfig.StateRecoveryStrategy"/>.
+    /// </summary>
+    /// <remarks>
+    /// After a reconnect, the server always drops the old watches.
+    /// <see cref="ReplayEvents"/> and <see cref="BatchStateUpdate"/> start watching those channels again.
+    /// <see cref="Disabled"/> does not - you must do that yourself.
+    /// </remarks>
+    public enum StateRecoveryStrategy
+    {
+        /// <summary>
+        /// Default.
+        ///
+        /// Missed events are replayed as normal events
+        /// (<see cref="StatefulModels.IStreamChannel.MessageReceived"/>,
+        /// <see cref="StatefulModels.IStreamChannel.ReactionAdded"/>, and so on).
+        /// The client also refreshes those channels and starts watching them again.
+        ///
+        /// Use this if your UI updates from per-event callbacks.
+        /// After a long disconnect on a busy channel this can replay many events at once
+        /// and cause a hitch.
+        /// </summary>
+        ReplayEvents = 0,
+
+        /// <summary>
+        /// Same recovery as <see cref="ReplayEvents"/>, but missed events update local state
+        /// without raising per-event callbacks. Listen to
+        /// <see cref="IStreamChatClient.StateRecovered"/> and rebuild your UI from channel state
+        /// (<see cref="StatefulModels.IStreamChannel.Messages"/>, and similar).
+        ///
+        /// Some events are still raised because they are not stored in channel state:
+        /// <see cref="StatefulModels.IStreamChannel.CustomEventReceived"/>,
+        /// <see cref="IStreamChatClient.ChannelDeleted"/>, and membership or invite notifications.
+        ///
+        /// Use this if a long disconnect causes a hitch when the app resumes.
+        /// </summary>
+        BatchStateUpdate = 1,
+
+        /// <summary>
+        /// The SDK does not restore state after a reconnect.
+        /// It does not refresh channels, does not start watching them again,
+        /// and does not raise <see cref="IStreamChatClient.StateRecovered"/>.
+        /// Local state and <see cref="IStreamChatClient.WatchedChannels"/> stay as they were
+        /// before the disconnect.
+        ///
+        /// Use this only if you handle recovery yourself. When the connection is
+        /// <see cref="LowLevelClient.ConnectionState.Connected"/> again, query the channels you need.
+        /// Example: <c>QueryChannelsAsync(new[] { ChannelFilter.Cid.In(cids) }, limit: 30)</c>.
+        /// That call refreshes state and starts watching.
+        /// Do not use <see cref="StatefulModels.IStreamChannel.WatchAsync"/> here:
+        /// <see cref="StatefulModels.IStreamChannel.IsWatched"/> is still true, so WatchAsync does nothing.
+        /// </summary>
+        Disabled = 2,
+    }
+}

Assets/Plugins/StreamChat/Core/Configs/StreamClientConfig.cs

@@ -12,5 +12,7 @@ public class StreamClientConfig : IStreamClientConfig
         public bool OptimisticMessageInsert { get; set; } = true;
 
         public MessageCacheWindow DefaultMessageCacheWindow { get; set; } = null;
+
+        public StateRecoveryStrategy StateRecoveryStrategy { get; set; } = Configs.StateRecoveryStrategy.ReplayEvents;
     }
 }

Assets/Plugins/StreamChat/Core/IStreamChatClient.cs

@@ -33,6 +33,24 @@ public interface IStreamChatClient : IDisposable, IStreamChatClientEventsListene
         /// </summary>
         event Action Disconnected;
 
+        /// <summary>
+        /// Raised once when reconnect recovery is done.
+        /// This includes full success, partial success, and cases with nothing to recover.
+        /// Not raised on the first login.
+        /// Not raised when <see cref="Configs.IStreamClientConfig.StateRecoveryStrategy"/> is
+        /// <see cref="Configs.StateRecoveryStrategy.Disabled"/>.
+        ///
+        /// Channels in <see cref="StreamStateRecoveredEventArgs.Channels"/> have fresh state and are watched again.
+        /// Cids in <see cref="StreamStateRecoveredEventArgs.UnrecoveredChannelCids"/> are still stale and not watched.
+        ///
+        /// Use this to rebuild your UI from channel state after a disconnect.
+        /// You need this for <see cref="Configs.StateRecoveryStrategy.BatchStateUpdate"/>,
+        /// because per-event callbacks do not fire during recovery.
+        /// It is also useful for <see cref="Configs.StateRecoveryStrategy.ReplayEvents"/>,
+        /// because some state updates after reconnect do not raise per-message callbacks.
+        /// </summary>
+        event StateRecoveredHandler StateRecovered;
+
         /// <summary>
         /// Event fired when connection state with Stream Chat server has changed
         /// </summary>
@@ -129,6 +147,12 @@ public interface IStreamChatClient : IDisposable, IStreamChatClientEventsListene
         /// methods may not be watched - check <see cref="IStreamChannel.IsWatched"/> on a specific
         /// channel to know its state.
         /// </para>
+        /// <para>
+        /// This list is cleared when the connection drops, because the server drops every watch.
+        /// Recovery fills it again.
+        /// If you read this list to restore watches yourself, do it before the disconnect,
+        /// or use <see cref="Configs.StateRecoveryStrategy.Disabled"/> so the list is not cleared.
+        /// </para>
         /// </summary>
         IReadOnlyList<IStreamChannel> WatchedChannels { get; }
 

Assets/Plugins/StreamChat/Core/LowLevelClient/HistorySyncApplyResult.cs

@@ -0,0 +1,21 @@
+using System;
+
+namespace StreamChat.Core.LowLevelClient
+{
+    /// <summary>
+    /// Result of applying one <c>/sync</c> history batch.
+    /// </summary>
+    internal sealed class HistorySyncApplyResult
+    {
+        /// <summary>
+        /// <c>created_at</c> of the newest event that applied, or <c>null</c>.
+        /// The <c>/sync</c> <c>last_sync_at</c> cursor advances to this.
+        /// </summary>
+        public DateTimeOffset? MaxAppliedCreatedAt { get; set; }
+
+        /// <summary>
+        /// Events that threw while applying. Skipped, not retried in this batch.
+        /// </summary>
+        public int FailedEventCount { get; set; }
+    }
+}