Basic vault prototype using OP_CAT

It is highlighted that the approach taken involves referencing the index of the input within the signature message, a method detailed within the full specification found in the Bitcoin Improvement Proposal 341 (full spec in bip341). A proposal is made suggesting that by enforcing the covenant input to be at a specific index (index 0 as per the example given), potential issues could be addressed effectively. This enforcement strategy implies that the current input index being set to 0 could serve as a solution to the problem at hand.