This seems like it might be unintended behaviour: I have a couple of active Pacts whose deficit has not been fully repaid. I have just purchased the "Siphoning" policy.
Expected consequences of selecting "Siphoning": (1) alicorns start being consumed, (2) necrocorns stop being consumed.
Actual consequences: (1) alicorns start being consumed (I assume), (2) necrocorns stop being consumed (I assume), BUT ALSO (3) necrocorn deficit stops reducing.
Since the necrocorn deficit makes my Pacts less effective and wouldn't have taken all that long to repay, the net effect of taking the Siphoning policy is to make things significantly worse, in a way it seems hard to believe it's meant to.
If this is intended, then it ought to be mentioned in the description of the Siphoning policy. My guess is that it isn't intended. It's hard to be sure from looking at the code -- the necrocorn-related code is pretty convoluted and not commented much so it's not obvious what its intent is.
(Possibly related: https://forum.kittensgame.com/post/950 "Siphoning policy not working?", which is the reason for the cautious "I assume"s above. Definitely not the same issue as I'm describing, though.)