mark
Claims a UTXO whose address matches any vault of this factory.
Called by the wallet for every UTXO it sees, against every contract. Match is by address equality against knownVaults, which spans the current destination, every receiving-map destination stamped with this contract's name (so deposits to drained or never-funded vaults are claimed too), and previously tagged UTXOs. The vault address commits to (chain, pubkey, unlockValue, index), so equality is an exact ownership test.
Spendability (has the unlock value been reached?) is deliberately NOT checked here — that belongs in filterInputs. A pre-unlock UTXO is still ours; marking it lets balance surface it and stops the wallet from spending it as a normal coin.
Side effects when matched:
Spendable.backingPayDestination is set to destination so signing uses this vault's template, constraint, and key material.
Spendable.contractId is set so forEachUtxo and balance find it.
Spendable.dirty is set so the wallet persists the change.