offers: update block height correctly.

As we can see from the previous test, l3 tells us why it rejected the payment:

```
lightningd-3 2024-11-19T03:56:27.151Z DEBUG   022d223620a359a47ff7f7ac447c85c46c923da53389221a0054c11c1e3ca31d59-chan#1: Failing HTLC because of an invalid payload (TLV 10 pos 104): cltv_expiry 136 > payment_constraint 130
```

It turns out, we were not updating the block height in the plugin!

Without this, when we create a (non-dummy) blinded path we set a
too-low CLTV restriction, and it doesn't work after a few blocks!

Note we were actually triggering this error in the xpay tests!

Reported-by: Vincenzo Palazzo
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Fixed: Offers: Receiving bolt12 payments where we have no public channels would fail a few blocks after startup.

plugins/offers.c

@@ -351,8 +351,13 @@ static struct command_result *block_added_notify(struct command *cmd,
 						 const char *buf,
 						 const jsmntok_t *params)
 {
-	json_scan(cmd, buf, params, "{block:{height:%}}",
-		  JSON_SCAN(json_to_u32, &blockheight));
+	const char *err = json_scan(cmd, buf, params, "{block_added:{height:%}}",
+				    JSON_SCAN(json_to_u32, &blockheight));
+	if (err)
+		plugin_err(cmd->plugin, "Failed to parse block_added (%.*s): %s",
+			   json_tok_full_len(params),
+			   json_tok_full(buf, params),
+			   err);
 	return notification_handled(cmd);
 }
 

tests/test_pay.py

@@ -5992,7 +5992,6 @@ def test_enableoffer(node_factory):
         l1.rpc.enableoffer(offer_id=offer1['offer_id'])
 
 
-@pytest.mark.xfail(strict=True)
 def test_offer_with_private_channels_multyhop2(node_factory):
     """We should be able to fetch an invoice through a private path and pay the invoice"""
     l1, l2, l3, l4, l5 = node_factory.line_graph(5, fundchannel=False)

tests/test_xpay.py

@@ -188,8 +188,7 @@ def test_xpay_simple(node_factory):
         l1.rpc.xpay(b11)
 
     # Failure from l3 (with blinded path)
-    # FIXME: We return wrong error here!
-    with pytest.raises(RpcError, match=r"Failed after 1 attempts\. Unexpected error \(invalid_onion_payload\) from intermediate node: disabling the invoice's blinded path \(0x0x0/[01]\) for this payment\. Then routing failed: We could not find a usable set of paths\.  The destination has disabled 1 of 1 channels, leaving capacity only 0msat of 10605000msat\."):
+    with pytest.raises(RpcError, match=r"Failed after 1 attempts. We got an error from inside the blinded path 0x0x0/1: we assume it means insufficient capacity. Then routing failed: We could not find a usable set of paths.  The shortest path is [0-9x]*->[0-9x]*->0x0x0, but 0x0x0/1 layer xpay-7 says max is 99999msat"):
         l1.rpc.xpay(b12)
 
     # Restart, try pay already paid one again.