So now i'm reverse-engineering the sample plugins (AGain) and drawing sequence diagrams like attched below. Do you know if something similar already exist? I've only seen the workflow diagrams in the documentation of vst3 sdk, but that didn't help much (well, now after my reverse-engineering i'm beginning to undertand those).
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looks like this approach is not so common, so I'd like to share my results, maybe it helps someone else as it helped me to understand how the host and the plugin work together... 