lightningd: use BIP86 derivation in p2wpkh_for_keyidx when available

When a peer doesn't support OPT_SHUTDOWN_ANYSEGWIT, we fall back to P2WPKH for the shutdown script. For BIP86 wallets, we need to use bip86_pubkey for derivation (matching p2tr_for_keyidx), otherwise the resulting script won't be recognized after restart.

Author: sangbida

lightningd/peer_control.c

@@ -203,7 +203,12 @@ u8 *p2wpkh_for_keyidx(const tal_t *ctx, struct lightningd *ld, u64 keyidx)
 {
 	struct pubkey shutdownkey;
 
-	bip32_pubkey(ld, &shutdownkey, keyidx);
+	/* Use BIP86 derivation if wallet has BIP86 base, otherwise use BIP32 */
+	if (ld->bip86_base) {
+		bip86_pubkey(ld, &shutdownkey, keyidx);
+	} else {
+		bip32_pubkey(ld, &shutdownkey, keyidx);
+	}
 	return scriptpubkey_p2wpkh(ctx, &shutdownkey);
 }