OP_CHECKCONTRACTVERIFY.

Would add a script command that lets coins carry a piece of data and set rules for the outputs they are spent to.

Today, limiting where coins can go next mostly relies on signing payments in advance. OP_CHECKCONTRACTVERIFY would let a coin hold committed data and check, when it is spent, that the new outputs follow set rules. It is meant as a building block for ideas such as vaults and shared coins like Ark.