Test trampoline fwd payload encoded as receive

diff --git a/lightning/src/ln/blinded_payment_tests.rs b/lightning/src/ln/blinded_payment_tests.rs
index 79697f0..d8dc094 100644
--- a/lightning/src/ln/blinded_payment_tests.rs
+++ b/lightning/src/ln/blinded_payment_tests.rs
@@ -1983,6 +1983,194 @@ fn test_trampoline_inbound_payment_decoding() {
 	};
 }
 
+#[test]
+fn test_trampoline_forward_payload_encoded_as_receive() {
+	// Test that we'll fail backwards as expected when receiving a well-formed blinded forward
+	// trampoline onion payload with no next hop present.
+	const TOTAL_NODE_COUNT: usize = 3;
+	let secp_ctx = Secp256k1::new();
+
+	let chanmon_cfgs = create_chanmon_cfgs(TOTAL_NODE_COUNT);
+	let node_cfgs = create_node_cfgs(TOTAL_NODE_COUNT, &chanmon_cfgs);
+	let node_chanmgrs = create_node_chanmgrs(TOTAL_NODE_COUNT, &node_cfgs, &vec![None; TOTAL_NODE_COUNT]);
+	let mut nodes = create_network(TOTAL_NODE_COUNT, &node_cfgs, &node_chanmgrs);
+
+	let (_, _, chan_id_alice_bob, _) = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 0);
+	let (_, _, chan_id_bob_carol, _) = create_announced_chan_between_nodes_with_value(&nodes, 1, 2, 1_000_000, 0);
+
+	for i in 0..TOTAL_NODE_COUNT { // connect all nodes' blocks
+		connect_blocks(&nodes[i], (TOTAL_NODE_COUNT as u32) * CHAN_CONFIRM_DEPTH + 1 - nodes[i].best_block_info().1);
+	}
+
+	let alice_node_id = nodes[0].node().get_our_node_id();
+	let bob_node_id = nodes[1].node().get_our_node_id();
+	let carol_node_id = nodes[2].node().get_our_node_id();
+
+	let alice_bob_scid = nodes[0].node().list_channels().iter().find(|c| c.channel_id == chan_id_alice_bob).unwrap().short_channel_id.unwrap();
+	let bob_carol_scid = nodes[1].node().list_channels().iter().find(|c| c.channel_id == chan_id_bob_carol).unwrap().short_channel_id.unwrap();
+
+	let amt_msat = 1000;
+	let (payment_preimage, payment_hash, _) = get_payment_preimage_hash(&nodes[2], Some(amt_msat), None);
+
+	// We need the session priv to construct an invalid onion packet later.
+	let override_random_bytes = [3; 32];
+	*nodes[0].keys_manager.override_random_bytes.lock().unwrap() = Some(override_random_bytes);
+
+	let outer_session_priv = SecretKey::from_slice(&override_random_bytes).unwrap();
+	let trampoline_session_priv = onion_utils::compute_trampoline_session_priv(&outer_session_priv);
+
+	// Create a blinded hop for the recipient that is encoded as a trampoline forward.
+	let carol_blinding_point = PublicKey::from_secret_key(&secp_ctx, &trampoline_session_priv);
+	let carol_blinded_hops =  {
+		let payee_tlvs = blinded_path::payment::TrampolineForwardTlvs {
+			next_trampoline: alice_node_id,
+			payment_constraints: PaymentConstraints {
+				max_cltv_expiry: u32::max_value(),
+				htlc_minimum_msat: amt_msat,
+			},
+			features: BlindedHopFeatures::empty(),
+			payment_relay: PaymentRelay {
+				cltv_expiry_delta: 0,
+				fee_proportional_millionths: 0,
+				fee_base_msat: 0,
+			},
+			next_blinding_override: None,
+		};
+
+		let carol_unblinded_tlvs = payee_tlvs.encode();
+		let path = [((carol_node_id, None), WithoutLength(&carol_unblinded_tlvs))];
+		blinded_path::utils::construct_blinded_hops(
+			&secp_ctx, path.into_iter(), &trampoline_session_priv,
+		)
+  };
+
+	let route = Route {
+		paths: vec![Path {
+			hops: vec![
+				// Bob
+				RouteHop {
+					pubkey: bob_node_id,
+					node_features: NodeFeatures::empty(),
+					short_channel_id: alice_bob_scid,
+					channel_features: ChannelFeatures::empty(),
+					fee_msat: 1000,
+					cltv_expiry_delta: 48,
+					maybe_announced_channel: false,
+				},
+
+				// Carol
+				RouteHop {
+					pubkey: carol_node_id,
+					node_features: NodeFeatures::empty(),
+					short_channel_id: bob_carol_scid,
+					channel_features: ChannelFeatures::empty(),
+					fee_msat: 0,
+					cltv_expiry_delta: 48,
+					maybe_announced_channel: false,
+				}
+			],
+			blinded_tail: Some(BlindedTail {
+				trampoline_hops: vec![
+					// Carol
+					TrampolineHop {
+						pubkey: carol_node_id,
+						node_features: Features::empty(),
+						fee_msat: amt_msat,
+						cltv_expiry_delta: 24,
+					},
+				],
+				hops: carol_blinded_hops,
+				blinding_point: carol_blinding_point,
+				excess_final_cltv_expiry_delta: 39,
+				final_value_msat: amt_msat,
+			})
+		}],
+		route_params: None,
+	};
+
+	nodes[0].node.send_payment_with_route(route.clone(), payment_hash, RecipientOnionFields::spontaneous_empty(), PaymentId(payment_hash.0)).unwrap();
+	check_added_monitors!(&nodes[0], 1);
+
+	let replacement_onion = {
+		// create a substitute onion where the last Trampoline hop is a forward
+		let recipient_onion_fields = RecipientOnionFields::spontaneous_empty();
+
+		let mut blinded_tail = route.paths[0].blinded_tail.clone().unwrap();
+
+		// append some dummy blinded hop so the intro hop looks like a forward
+		blinded_tail.hops.push(BlindedHop {
+			blinded_node_id: alice_node_id,
+			encrypted_payload: vec![],
+		});
+
+		let (mut trampoline_payloads, outer_total_msat, outer_starting_htlc_offset) = onion_utils::build_trampoline_onion_payloads(&blinded_tail, amt_msat, &recipient_onion_fields, 32, &None).unwrap();
+
+		// pop the last dummy hop
+		trampoline_payloads.pop();
+
+		let trampoline_onion_keys = onion_utils::construct_trampoline_onion_keys(&secp_ctx, &route.paths[0].blinded_tail.as_ref().unwrap(), &trampoline_session_priv);
+		let trampoline_packet = onion_utils::construct_trampoline_onion_packet(
+			trampoline_payloads,
+			trampoline_onion_keys,
+			override_random_bytes,
+			&payment_hash,
+			None,
+		).unwrap();
+
+		let (outer_payloads, _, _) = onion_utils::build_onion_payloads(&route.paths[0], outer_total_msat, &recipient_onion_fields, outer_starting_htlc_offset, &None, None, Some(trampoline_packet)).unwrap();
+		let outer_onion_keys = onion_utils::construct_onion_keys(&secp_ctx, &route.clone().paths[0], &outer_session_priv);
+		let outer_packet = onion_utils::construct_onion_packet(
+			outer_payloads,
+			outer_onion_keys,
+			override_random_bytes,
+			&payment_hash,
+		).unwrap();
+
+		outer_packet
+	};
+
+	let mut events = nodes[0].node.get_and_clear_pending_msg_events();
+	assert_eq!(events.len(), 1);
+	let mut first_message_event = remove_first_msg_event_to_node(&nodes[1].node.get_our_node_id(), &mut events);
+	let mut update_message = match first_message_event {
+		MessageSendEvent::UpdateHTLCs { ref mut updates, .. } => {
+			assert_eq!(updates.update_add_htlcs.len(), 1);
+			updates.update_add_htlcs.get_mut(0)
+		},
+		_ => panic!()
+	};
+	update_message.map(|msg| {
+		msg.onion_routing_packet = replacement_onion.clone();
+	});
+
+	let route: &[&Node] = &[&nodes[1], &nodes[2]];
+	let args = PassAlongPathArgs::new(&nodes[0], route, amt_msat, payment_hash, first_message_event)
+		.with_payment_preimage(payment_preimage)
+		.without_claimable_event()
+		.expect_failure(HTLCHandlingFailureType::InvalidOnion);
+	do_pass_along_path(args);
+
+	{
+		let unblinded_node_updates = get_htlc_update_msgs!(nodes[2], nodes[1].node.get_our_node_id());
+		nodes[1].node.handle_update_fail_htlc(
+			nodes[2].node.get_our_node_id(), &unblinded_node_updates.update_fail_htlcs[0]
+		);
+		do_commitment_signed_dance(&nodes[1], &nodes[2], &unblinded_node_updates.commitment_signed, true, false);
+	}
+	{
+		let unblinded_node_updates = get_htlc_update_msgs!(nodes[1], nodes[0].node.get_our_node_id());
+		nodes[0].node.handle_update_fail_htlc(
+			nodes[1].node.get_our_node_id(), &unblinded_node_updates.update_fail_htlcs[0]
+		);
+		do_commitment_signed_dance(&nodes[0], &nodes[1], &unblinded_node_updates.commitment_signed, false, false);
+	}
+	{
+		let payment_failed_conditions = PaymentFailedConditions::new()
+			.expected_htlc_error_data(LocalHTLCFailureReason::InvalidOnionPayload, &[0; 0]);
+		expect_payment_failed_conditions(&nodes[0], payment_hash, true, payment_failed_conditions);
+	}
+}
+
 fn do_test_trampoline_single_hop_receive(success: bool) {
 	const TOTAL_NODE_COUNT: usize = 3;
 	let secp_ctx = Secp256k1::new();