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When a node disconnects, serveLongPoll defers a cleanup that starts a grace period goroutine. This goroutine polls batcher.IsConnected() and, if the node has not reconnected within ~10 seconds, calls state.Disconnect() to mark it offline. A TOCTOU race exists: the node can reconnect (calling Connect()) between the IsConnected check and the Disconnect() call, causing the stale Disconnect() to overwrite the new session's online status. Fix with a monotonic per-node generation counter: - State.Connect() increments the counter and returns the current generation alongside the change list. - State.Disconnect() accepts the generation from the caller and rejects the call if a newer generation exists, making stale disconnects from old sessions a no-op. - serveLongPoll captures the generation at Connect() time and passes it to Disconnect() in the deferred cleanup. - RemoveNode's return value is now checked: if another session already owns the batcher slot (reconnect happened), the old session skips the grace period entirely. Update batcher_test.go to track per-node connect generations and pass them through to Disconnect(), matching production behavior. Fixes the following test failures: - server_state_online_after_reconnect_within_grace - update_history_no_false_offline - nodestore_correct_after_rapid_reconnect - rapid_reconnect_peer_never_sees_offline