Main path: n_sigs of the main keys (never HTLC, which also needs the preimage). After the
locktime: n_sigs_refund of the refund keys, or none without them. Keys match by x coordinate,
and through p2pk_e for a blinded proof (NUT-28).
Throws
If the secret is not P2PK/HTLC or its tags break the NUT-11 rules.
Whether
privkeyscan spend a P2PK or HTLC locked proof atnow, without a preimage.