message: actually call the hook lol
diff: @@ -883,6 +883,9 @@ public:
  }
  void handle(const uint8_t* input, size_t input_length, StreamSink* output) final {
  default_readwrite_endpoint_handler<TProperty>(property_, input, input_length, output);
  + if (written_hook_ != nullptr) {
  + written_hook_(ctx_);
  + }
  }
  /*void handle(const uint8_t* input, size_t input_length, StreamSink* output) {
  handle(input, input_length, output);
  