Boarding UTXOs grouped by the boarding address they sit on, carrying that
address's signer association explicitly. Returned by
ReadonlyWallet.getBoardingUtxosForSigners because a flat
ExtendedCoin cannot carry the signer: it retains only the encoded
leaves/tapTree the spend needs, not the owning DefaultVtxo.Script (and so
not its serverPubKey or CSV delay). The deprecated-signer boarding
classification reads both back from this group (Section 7).
Boarding UTXOs grouped by the boarding address they sit on, carrying that address's signer association explicitly. Returned by ReadonlyWallet.getBoardingUtxosForSigners because a flat ExtendedCoin cannot carry the signer: it retains only the encoded leaves/tapTree the spend needs, not the owning
DefaultVtxo.Script(and so not itsserverPubKeyor CSV delay). The deprecated-signer boarding classification reads both back from this group (Section 7).