UTXO selection/createTx: support changeOutput (script-based change)

[carloscjdev]

selectUTXO(..., { createTx: true }) requires changeAddress. Allow a richer changeOutput object so change can target script-only outputs (P2WSH, Taproot trees, P2A, etc.) without deriving an address.

API

type SelectUtxoOpts = {
  changeAddress?: string; // existing
  changeOutput?: {
    script?: Bytes;
    redeemScript?: Bytes;
    witnessScript?: Bytes;
    tapInternalKey?: Bytes;
    bip32Derivation?: [Bytes, { fingerprint: number; path: number[] }][];
  }; // NEW
  feePerByte: bigint;
  bip69?: boolean;
  createTx?: boolean;
  network?: Network;
};

Example

const ms = btc.p2wsh(btc.p2ms(2, [pub1, pub2, pub3]));
const sel = btc.selectUTXO(utxo, outs, 'default', {
  changeOutput: { script: ms.script, witnessScript: ms.witnessScript },
  feePerByte: 2n,
  createTx: true,
});

Behavior

• If changeOutput is set → use it for change and ignore changeAddress.
• Backward compatible when only changeAddress is provided.