Add test for monitor update after funding spend

diff --git a/lightning/src/ln/chanmon_update_fail_tests.rs b/lightning/src/ln/chanmon_update_fail_tests.rs
index 11fc8ac..87856c9 100644
--- a/lightning/src/ln/chanmon_update_fail_tests.rs
+++ b/lightning/src/ln/chanmon_update_fail_tests.rs
@@ -16,7 +16,7 @@ use crate::chain::chaininterface::LowerBoundedFeeEstimator;
 use crate::chain::chainmonitor::ChainMonitor;
 use crate::chain::channelmonitor::{ChannelMonitor, MonitorEvent, ANTI_REORG_DELAY};
 use crate::chain::transaction::OutPoint;
-use crate::chain::{ChannelMonitorUpdateStatus, Listen, Watch};
+use crate::chain::{ChannelMonitorUpdateStatus, Confirm, Listen, Watch};
 use crate::events::{ClosureReason, Event, HTLCHandlingFailureType, PaymentPurpose};
 use crate::ln::channel::AnnouncementSigsState;
 use crate::ln::channelmanager::{PaymentId, RAACommitmentOrder};
@@ -5421,3 +5421,72 @@ fn test_late_counterparty_commitment_update_after_holder_commitment_spend() {
 fn test_late_counterparty_commitment_update_after_holder_commitment_spend_dust() {
 	do_test_late_counterparty_commitment_update_after_holder_commitment_spend(true);
 }
+
+#[test]
+#[should_panic(
+	expected = "Watch::update_channel returned Completed while prior updates are still InProgress"
+)]
+fn test_monitor_update_fail_after_funding_spend() {
+	// When a counterparty commitment transaction confirms (funding spend), the
+	// ChannelMonitor sets funding_spend_seen. If a commitment_signed from the
+	// counterparty is then processed (a race between chain events and message
+	// processing), update_monitor returns Err because no_further_updates_allowed()
+	// is true. ChainMonitor overrides the result to InProgress, permanently
+	// freezing the channel. A subsequent preimage claim returning Completed then
+	// triggers the per-channel assertion.
+	let chanmon_cfgs = create_chanmon_cfgs(2);
+	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
+	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
+	let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+
+	let node_a_id = nodes[0].node.get_our_node_id();
+
+	let (_, _, chan_id, _) = create_announced_chan_between_nodes(&nodes, 0, 1);
+
+	// Route payment 1 fully so B can claim it later.
+	let (payment_preimage_1, _payment_hash_1, ..) =
+		route_payment(&nodes[0], &[&nodes[1]], 1_000_000);
+
+	// Get A's commitment tx (this is the "counterparty" commitment from B's perspective).
+	let as_commitment_tx = get_local_commitment_txn!(nodes[0], chan_id);
+	assert_eq!(as_commitment_tx.len(), 1);
+
+	// Confirm A's commitment tx on B's chain_monitor ONLY (not on B's ChannelManager).
+	// This sets funding_spend_seen in the monitor, making no_further_updates_allowed() true.
+	let (block_hash, height) = nodes[1].best_block_info();
+	let block = create_dummy_block(block_hash, height + 1, vec![as_commitment_tx[0].clone()]);
+	let txdata: Vec<_> = block.txdata.iter().enumerate().collect();
+	nodes[1].chain_monitor.chain_monitor.transactions_confirmed(&block.header, &txdata, height + 1);
+
+	// Send payment 2 from A to B.
+	let (route, payment_hash_2, _, payment_secret_2) =
+		get_route_and_payment_hash!(&nodes[0], nodes[1], 1_000_000);
+	nodes[0]
+		.node
+		.send_payment_with_route(
+			route,
+			payment_hash_2,
+			RecipientOnionFields::secret_only(payment_secret_2, 1_000_000),
+			PaymentId(payment_hash_2.0),
+		)
+		.unwrap();
+	check_added_monitors(&nodes[0], 1);
+
+	let mut events = nodes[0].node.get_and_clear_pending_msg_events();
+	assert_eq!(events.len(), 1);
+	let payment_event = SendEvent::from_event(events.remove(0));
+
+	nodes[1].node.handle_update_add_htlc(node_a_id, &payment_event.msgs[0]);
+
+	// B processes commitment_signed. The monitor's update_monitor succeeds on the
+	// update steps, but returns Err at the end because no_further_updates_allowed()
+	// is true (funding_spend_seen). ChainMonitor overrides the result to InProgress.
+	nodes[1].node.handle_commitment_signed(node_a_id, &payment_event.commitment_msg[0]);
+	check_added_monitors(&nodes[1], 1);
+	assert!(nodes[1].node.get_and_clear_pending_msg_events().is_empty());
+
+	// B claims payment 1. The PaymentPreimage monitor update returns Completed
+	// (update_monitor succeeds for preimage, and persister returns Completed),
+	// but the prior InProgress from the commitment_signed is still pending.
+	nodes[1].node.claim_funds(payment_preimage_1);
+}