lightningd: more debugging around fake_channeld failure.

```
2024-12-16T23:16:16.4874420Z lightningd-1 2024-12-16T22:45:14.068Z UNUSUAL 022d223620a359a47ff7f7ac447c85c46c923da53389221a0054c11c1e3ca31d59-channeld-chan#1: Adding HTLC 18446744073709551615 too slow: killing connection
```

This implies that we don't transition the HTLC correctly.

Signed-off-by: Rusty Russell <[email protected]>

lightningd/peer_htlcs.c

@@ -722,6 +722,7 @@ const u8 *send_htlc_out(const tal_t *ctx,
 						 *houtp, time_from_sec(30),
 						 htlc_offer_timeout,
 						 *houtp);
+		log_debug(out->log, "Added timer for htlc %p", *houtp);
 	}
 
 	msg = towire_channeld_offer_htlc(out, amount, cltv, payment_hash,
@@ -2000,6 +2001,8 @@ static bool update_out_htlc(struct channel *channel,
 
 	/* First transition into commitment; now it outlives peer. */
 	if (newstate == SENT_ADD_COMMIT) {
+		log_debug(channel->log, "Removing timer for htlc %p %"PRIu64" (dbid %"PRIu64")",
+			  hout, hout->key.id, hout->dbid);
 		tal_del_destructor(hout, destroy_hout_subd_died);
 		hout->timeout = tal_free(hout->timeout);
 		tal_steal(ld, hout);
@@ -2109,13 +2112,17 @@ void peer_sending_commitsig(struct channel *channel, const u8 *msg)
 		return;
 	}
 
+	log_debug(channel->log, "sending_commitsig with %zu changes",
+		  tal_count(changed_htlcs));
 	for (i = 0; i < tal_count(changed_htlcs); i++) {
+		log_debug(channel->log, ".. changed htlc %"PRIu64" -> %s",
+			  changed_htlcs[i].id, htlc_state_name(changed_htlcs[i].newstate));
+
 		if (!changed_htlc(channel, changed_htlcs + i)) {
 			channel_internal_error(channel,
 				   "channel_sending_commitsig: update failed");
 			return;
 		}
-
 		/* While we're here, sanity check added ones are in
 		 * ascending order. */
 		if (changed_htlcs[i].newstate == SENT_ADD_COMMIT) {