Basic vault prototype using OP_CAT

It is emphasized that for a 'complete withdrawal' to be properly enforced, it is crucial to ensure that the input index = 0. This stipulation is necessary to prevent a scenario where two input Unspent Transaction Outputs (UTXOs) in a 'trigger withdrawal' state could be misused. Specifically, one could be utilized as a 'contract input' while the other serves as a 'fee-paying input', even if they originate from different vaults. Such an arrangement poses the risk of the second UTXO being drained to the miner as a fee, thereby circumventing intended security measures and protocols. This insight underscores the importance of stringent criteria and checks in the complete withdrawal phase to safeguard against potential exploitation and to maintain the integrity of the transaction process.