What is the 'additive-only spending' pattern in Kaspa?

Kaspa's scripting system can lock a coin balance so that it can only grow — never be drained — unless the original owner signs off. This works through a script with two spending paths: the owner can always withdraw by providing a valid signature, but anyone else can only move the funds if they immediately return them to the exact same address with a higher value, by at least a pre-set threshold amount. A UTXO (an unspent coin balance) therefore acts like a one-way lock-box: anyone can top it up, but value extraction is blocked without the owner's authorization. For a beginner, this demonstrates how Kaspa's scripting layer can enforce real-world deposit rules — such as a savings vault or collateral account — without relying on a trusted middleman.