OptionalsourceRaw wire bytes of the ark transaction that created this VTXO, attached as the PrevArkTx field on input 0.
An override, not the only channel: covenant spends resolve the previous tx of every input through the client's indexer. Supply it when the tx is not yet indexable — a recursive covenant spending the output of an ark tx the caller just built — and the resolved value is suppressed for input 0.
A spendable coin (VTXO) — outpoint + value.