The RPC and sync library mechanisms were removed for now; they never really worked and contained several obvious bugs. Need to consider if syncs are useful at all during the compose time, or just used during intro.
There is a new "sync" opcode that saves the top-most signal every 256 samples to the new "syncBuffer" output. Additionally, you can enable saving the current fractional row as sync[0], avoiding calculating the beat in the shader, but also calculating the beat correctly when the beat is modulated.