return sequenceNumber.incrementAndGet();
    }
    
    public void updateHeartbeat() {
        this.lastHeartbeat = System.currentTimeMillis();
    }
    
    public boolean isExpired(long timeoutMs) {
        return System.currentTimeMillis() - lastHeartbeat > timeoutMs;
    }
    
    // Getters and setters...
    public String getRegistrationId() { return registrationId; }