How to access AudioBuffer after AudioProcessorGraph->processBlock?

I’m applying this tutorial to a command-line VST renderer. For reference, this tool uses processBlock and then immediately in fillAudioFeatures accesses the audioBuffer to append to a std::vector<double>.

This method seems better than dealing with a callback function or an audio listener.

Now I’m trying to do the same thing but with an AudioProcessorGraph instead of an audio plugin. The audio input node goes to the OscillatorProcessor node, which goes to the audio output node. I’ve done prepareToPlay and setPlayConfigDetails with 2 input/2 output channels for both the OscillatorProcessor and AudioProcessorGraph. When I call mainProcessor->processBlock and check the AudioBuffer afterwards, it’s all zeros. However, I can confirm with a hacky std::cout that the OscillatorProcessor node is generating non zero values.

Is the solution to insert a “passthrough” AudioProcessor right before the out node? This processor would append to std::vector<double>.