lightningd: don't let spendable_msat go wumbo.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/peer_control.c

@@ -688,6 +688,10 @@ static void json_add_channel(struct lightningd *ld,
 			     channel->channel_info.their_config.htlc_minimum))
 		spendable = AMOUNT_MSAT(0);
 
+	/* We can't offer an HTLC over the max payment threshold either. */
+	if (amount_msat_greater(spendable, get_chainparams(ld)->max_payment))
+		spendable = get_chainparams(ld)->max_payment;
+
 	json_add_amount_msat_compat(response, spendable,
 				    "spendable_msatoshi", "spendable_msat");
 	json_add_amount_msat_compat(response,

tests/test_pay.py

@@ -2124,7 +2124,6 @@ def test_channel_spendable_large(node_factory, bitcoind):
     l1.rpc.waitsendpay(payment_hash, TIMEOUT)
 
 
-@pytest.mark.xfail(strict=True)
 def test_channel_spendable_capped(node_factory, bitcoind):
     """Test that spendable_msat is capped at 2^32-1"""
     sats = 16777215