diff --git a/fuzz/src/chanmon_consistency.rs b/fuzz/src/chanmon_consistency.rs
index 519ae515e7f..113d52f7576 100644
--- a/fuzz/src/chanmon_consistency.rs
+++ b/fuzz/src/chanmon_consistency.rs
@@ -14,9 +14,10 @@
 //! To test this we stand up a network of three nodes and read bytes from the fuzz input to denote
 //! actions such as sending payments, handling events, or changing monitor update return values on
 //! a per-node basis. This should allow it to find any cases where the ordering of actions results
-//! in us getting out of sync with ourselves, and, assuming at least one of our recieve- or
-//! send-side handling is correct, other peers. We consider it a failure if any action results in a
-//! channel being force-closed.
+//! in us getting out of sync with ourselves, and, assuming at least one of our receive- or
+//! send-side handling is correct, other peers. We consider it a failure if any action results in
+//! a channel being force-closed. The fuzzer also models transaction relay through a harness
+//! mempool, making splice confirmation and block delivery closer to normal node behavior.
 
 use bitcoin::amount::Amount;
 use bitcoin::constants::genesis_block;
@@ -27,6 +28,7 @@ use bitcoin::script::{Builder, ScriptBuf};
 use bitcoin::transaction::Version;
 use bitcoin::transaction::{Transaction, TxOut};
 use bitcoin::FeeRate;
+use bitcoin::OutPoint as BitcoinOutPoint;
 
 use bitcoin::block::Header;
 use bitcoin::hash_types::Txid;
@@ -41,7 +43,7 @@ use lightning::chain;
 use lightning::chain::chaininterface::{
 	BroadcasterInterface, ConfirmationTarget, FeeEstimator, TransactionType,
 };
-use lightning::chain::channelmonitor::ChannelMonitor;
+use lightning::chain::channelmonitor::{ChannelMonitor, ANTI_REORG_DELAY};
 use lightning::chain::{
 	chainmonitor, channelmonitor, BlockLocator, ChannelMonitorUpdateStatus, Confirm, Watch,
 };
@@ -103,6 +105,17 @@ use std::sync::{Arc, Mutex};
 
 const MAX_FEE: u32 = 10_000;
 const MAX_SETTLE_ITERATIONS: usize = 256;
+// Each wallet is seeded with enough confirmed UTXOs that repeated splice
+// transactions don't run out of inputs mid-run.
+const NUM_WALLET_UTXOS: u32 = 50;
+// A single fuzz byte can mine more than one block so a corpus entry does not
+// need long runs of identical "mine one block" commands to reach CSV or CLTV
+// boundaries. Mining commands are capped in `safe_mine_block_count` if
+// unresolved HTLCs are near expiry.
+const MINE_BLOCK_COUNTS: [u32; 8] = [1, 2, 3, 6, 12, 24, 48, 144];
+// Finish-time relay/mining rounds are capped so cleanup cannot spin forever.
+const MAX_FINISH_RELAY_MINE_ROUNDS: usize = 32;
+
 struct FuzzEstimator {
 	ret_val: atomic::AtomicU32,
 }
@@ -184,9 +197,14 @@ impl BroadcasterInterface for TestBroadcaster {
 struct ChainState {
 	blocks: Vec<(Header, Vec<Transaction>)>,
 	confirmed_txids: HashSet<Txid>,
-	/// Unconfirmed transactions (e.g., splice txs). Conflicting RBF candidates may coexist;
-	/// `confirm_pending_txs` determines which one confirms.
+	/// Unconfirmed transactions admitted to the mempool, in valid block order:
+	/// every input is either confirmed already or created by an earlier
+	/// transaction in this vector.
 	pending_txs: Vec<(Txid, Transaction)>,
+	/// Unspent outputs created by confirmed transactions. Mempool admission
+	/// checks inputs against this set, adjusted for outputs created and spent
+	/// by the transactions already in `pending_txs`.
+	utxos: HashSet<BitcoinOutPoint>,
 }
 
 impl ChainState {
@@ -197,6 +215,7 @@ impl ChainState {
 			blocks: vec![(genesis_header, Vec::new())],
 			confirmed_txids: HashSet::new(),
 			pending_txs: Vec::new(),
+			utxos: HashSet::new(),
 		}
 	}
 
@@ -204,81 +223,223 @@ impl ChainState {
 		(self.blocks.len() - 1) as u32
 	}
 
-	fn is_outpoint_spent(&self, outpoint: &bitcoin::OutPoint) -> bool {
-		self.blocks.iter().any(|(_, txs)| {
-			txs.iter().any(|tx| tx.input.iter().any(|input| input.previous_output == *outpoint))
+	fn is_unspent(&self, outpoint: &BitcoinOutPoint) -> bool {
+		self.utxos.contains(outpoint)
+	}
+
+	fn confirmed_output(&self, outpoint: &BitcoinOutPoint) -> Option<&TxOut> {
+		if !self.confirmed_txids.contains(&outpoint.txid) {
+			return None;
+		}
+		self.blocks.iter().find_map(|(_, txs)| {
+			txs.iter().find_map(|tx| {
+				if tx.compute_txid() == outpoint.txid {
+					tx.output.get(outpoint.vout as usize)
+				} else {
+					None
+				}
+			})
 		})
 	}
 
-	fn confirm_tx(&mut self, tx: Transaction) -> bool {
-		let txid = tx.compute_txid();
-		if self.confirmed_txids.contains(&txid) {
-			return false;
+	// Initial channel funding is represented by a no-input transaction. It is
+	// not a valid Bitcoin transaction, but it gives LDK a stable funding
+	// outpoint without modeling coin selection during channel setup.
+	fn is_synthetic_funding_tx(tx: &Transaction) -> bool {
+		!tx.is_coinbase() && tx.input.is_empty()
+	}
+
+	// Checks whether a transaction spends an input twice or spends an output
+	// not present in `utxos`.
+	fn has_invalid_inputs(tx: &Transaction, utxos: &HashSet<BitcoinOutPoint>) -> bool {
+		let mut spent_inputs = HashSet::new();
+		for input in &tx.input {
+			if !spent_inputs.insert(input.previous_output) {
+				return true;
+			}
+			if !utxos.contains(&input.previous_output) {
+				return true;
+			}
+		}
+		false
+	}
+
+	fn apply_tx_to_utxos(&mut self, txid: Txid, tx: &Transaction) {
+		for input in &tx.input {
+			self.utxos.remove(&input.previous_output);
 		}
-		if tx.input.iter().any(|input| self.is_outpoint_spent(&input.previous_output)) {
-			return false;
+		for idx in 0..tx.output.len() {
+			self.utxos.insert(BitcoinOutPoint { txid, vout: idx as u32 });
 		}
-		self.confirmed_txids.insert(txid);
+	}
 
+	fn mine_block(&mut self, txs: Vec<Transaction>) {
 		let prev_hash = self.blocks.last().unwrap().0.block_hash();
 		let header = create_dummy_header(prev_hash, 42);
-		self.blocks.push((header, vec![tx]));
+		self.blocks.push((header, txs));
+	}
 
-		for _ in 0..5 {
-			let prev_hash = self.blocks.last().unwrap().0.block_hash();
-			let header = create_dummy_header(prev_hash, 42);
-			self.blocks.push((header, Vec::new()));
+	fn mine_empty_blocks(&mut self, count: u32) {
+		for _ in 0..count {
+			self.mine_block(Vec::new());
 		}
-		true
 	}
 
-	/// Add a transaction to the pending pool (mempool). Multiple conflicting transactions (RBF
-	/// candidates) may coexist; `confirm_pending_txs` selects which one to confirm.
-	fn add_pending_tx(&mut self, tx: Transaction) {
-		self.pending_txs.push((tx.compute_txid(), tx));
+	// Mines a setup transaction directly into a block, bypassing the mempool,
+	// and buries it to `depth`. Wallet seeding and synthetic funding
+	// transactions are not relayable, so they cannot go through normal
+	// admission.
+	fn mine_setup_tx_to_depth(&mut self, tx: Transaction, depth: u32) {
+		assert!(
+			tx.is_coinbase() || Self::is_synthetic_funding_tx(&tx),
+			"direct setup mining is only for coinbase and synthetic funding transactions: {:?}",
+			tx,
+		);
+		let txid = tx.compute_txid();
+		assert!(
+			self.confirmed_txids.insert(txid),
+			"direct setup transaction was already confirmed: {:?}",
+			tx,
+		);
+		self.apply_tx_to_utxos(txid, &tx);
+
+		self.mine_block(vec![tx]);
+		self.mine_empty_blocks(depth.saturating_sub(1));
 	}
 
-	/// Confirm pending transactions in a single block, selecting deterministically among
-	/// conflicting RBF candidates. Sorting by txid ensures the winner is determined by fuzz input
-	/// content. Transactions that double-spend an already-confirmed outpoint are skipped.
-	fn confirm_pending_txs(&mut self) {
-		let mut txs = std::mem::take(&mut self.pending_txs);
-		txs.sort_by_key(|(txid, _)| *txid);
+	// Attempts to admit a broadcast transaction to the mempool, enforcing
+	// locktime, input, and RBF rules. Mining later confirms the whole mempool
+	// without further selection.
+	fn admit_tx_to_mempool(&mut self, tx: Transaction) {
+		let txid = tx.compute_txid();
+		let lock_time = tx.lock_time.to_consensus_u32();
+		let locktime_enabled =
+			tx.input.iter().any(|input| input.sequence.enables_absolute_lock_time());
 
-		let mut confirmed = Vec::new();
-		let mut spent_outpoints = Vec::new();
-		for (txid, tx) in txs {
-			if self.confirmed_txids.contains(&txid) {
-				continue;
-			}
-			if tx.input.iter().any(|input| {
-				self.is_outpoint_spent(&input.previous_output)
-					|| spent_outpoints.contains(&input.previous_output)
-			}) {
-				continue;
+		let is_ldk_commitment_obscured_locktime =
+			tx.input.len() == 1 && tx.input[0].sequence.0 >> 24 == 0x80 && lock_time >> 24 == 0x20;
+
+		let immature_absolute_locktime =
+			locktime_enabled && tx.lock_time.is_block_height() && self.tip_height() < lock_time;
+		assert!(
+			!immature_absolute_locktime,
+			"broadcast immature locktime transaction into chanmon harness mempool: {:?}",
+			tx,
+		);
+
+		let unmodeled_time_locktime = locktime_enabled
+			&& tx.lock_time.is_block_time()
+			&& !is_ldk_commitment_obscured_locktime;
+		assert!(
+			!unmodeled_time_locktime,
+			"broadcast time-locked transaction into chanmon harness mempool: {:?}",
+			tx,
+		);
+
+		assert!(
+			!tx.is_coinbase() && !Self::is_synthetic_funding_tx(&tx),
+			"setup-only transaction entered chanmon harness mempool: {:?}",
+			tx,
+		);
+
+		if self.confirmed_txids.contains(&txid) {
+			return;
+		}
+		if self.pending_txs.iter().any(|(pending_txid, _)| *pending_txid == txid) {
+			return;
+		}
+
+		// Fee-rate policy is not modeled, so among conflicting RBF candidates
+		// the last one relayed wins.
+		let mut conflicting_pending_txids = HashSet::new();
+		for (pending_txid, pending_tx) in &self.pending_txs {
+			let signals_rbf = pending_tx.input.iter().any(|input| input.sequence.is_rbf());
+			let conflicts_with_new_tx = pending_tx.input.iter().any(|pending_input| {
+				tx.input.iter().any(|input| input.previous_output == pending_input.previous_output)
+			});
+			if conflicts_with_new_tx {
+				if !signals_rbf {
+					return;
+				}
+				conflicting_pending_txids.insert(*pending_txid);
 			}
-			self.confirmed_txids.insert(txid);
-			for input in &tx.input {
-				spent_outpoints.push(input.previous_output);
+		}
+		if !conflicting_pending_txids.is_empty() {
+			let mut removed_outputs = HashSet::new();
+			let mut retained_txs = Vec::new();
+			for (pending_txid, pending_tx) in self.pending_txs.drain(..) {
+				let direct_conflict = conflicting_pending_txids.contains(&pending_txid);
+				let spends_removed_tx = pending_tx
+					.input
+					.iter()
+					.any(|input| removed_outputs.contains(&input.previous_output));
+				if direct_conflict || spends_removed_tx {
+					for idx in 0..pending_tx.output.len() {
+						removed_outputs
+							.insert(BitcoinOutPoint { txid: pending_txid, vout: idx as u32 });
+					}
+				} else {
+					retained_txs.push((pending_txid, pending_tx));
+				}
 			}
-			confirmed.push(tx);
+			self.pending_txs = retained_txs;
 		}
 
-		if confirmed.is_empty() {
+		// Build the UTXO set this transaction would see if the current mempool
+		// confirmed.
+		let mut available_utxos = self.utxos.clone();
+		for (pending_txid, pending_tx) in &self.pending_txs {
+			for input in &pending_tx.input {
+				available_utxos.remove(&input.previous_output);
+			}
+			for idx in 0..pending_tx.output.len() {
+				available_utxos.insert(BitcoinOutPoint { txid: *pending_txid, vout: idx as u32 });
+			}
+		}
+		if Self::has_invalid_inputs(&tx, &available_utxos) {
 			return;
 		}
+		self.pending_txs.push((txid, tx));
+	}
 
-		let prev_hash = self.blocks.last().unwrap().0.block_hash();
-		let header = create_dummy_header(prev_hash, 42);
-		self.blocks.push((header, confirmed));
-
-		for _ in 0..5 {
-			let prev_hash = self.blocks.last().unwrap().0.block_hash();
-			let header = create_dummy_header(prev_hash, 42);
-			self.blocks.push((header, Vec::new()));
+	fn relay_transactions(&mut self, txs: Vec<Transaction>) {
+		for tx in txs {
+			self.admit_tx_to_mempool(tx);
 		}
 	}
 
+	// Mines `count` blocks, confirming the current mempool in the first block.
+	fn mine_blocks(&mut self, count: u32) -> Vec<Transaction> {
+		assert!(count > 0, "mining zero blocks should not be requested");
+
+		let mempool_txs = std::mem::take(&mut self.pending_txs);
+		let confirmed_txs = if mempool_txs.is_empty() {
+			self.mine_empty_blocks(1);
+			Vec::new()
+		} else {
+			let mut confirmed = Vec::new();
+			for (txid, tx) in mempool_txs {
+				assert!(
+					!Self::has_invalid_inputs(&tx, &self.utxos),
+					"mempool transaction was no longer valid at mining time: {:?}",
+					tx,
+				);
+				assert!(
+					self.confirmed_txids.insert(txid),
+					"mempool transaction was already confirmed at mining time: {:?}",
+					tx,
+				);
+				self.apply_tx_to_utxos(txid, &tx);
+				confirmed.push(tx);
+			}
+			let confirmed_txs = confirmed.clone();
+			self.mine_block(confirmed);
+			confirmed_txs
+		};
+		self.mine_empty_blocks(count - 1);
+		confirmed_txs
+	}
+
 	fn block_at(&self, height: u32) -> &(Header, Vec<Transaction>) {
 		&self.blocks[height as usize]
 	}
@@ -775,7 +936,13 @@ fn assert_disconnect_action(action: &msgs::ErrorAction) -> (&msgs::WarningMessag
 	// Since sending/receiving messages may be delayed, `timer_tick_occurred` may cause a node to
 	// disconnect their counterparty if they're expecting a timely response.
 	if let msgs::ErrorAction::DisconnectPeerWithWarning { ref msg } = action {
-		let is_quiescent_msg = msg.data.contains("already sent splice_locked, cannot RBF");
+		// A splice can be refused mid-negotiation when the post-splice balance would
+		// breach the channel reserve. Like the RBF case, this leaves the channel
+		// quiescent, so both sides must exit quiescence afterwards.
+		let is_quiescent_msg = msg.data.contains("already sent splice_locked, cannot RBF")
+			|| msg.data.contains("has a confirmed pending splice, cannot RBF")
+			|| msg.data.contains("smaller than their selected v2 reserve")
+			|| msg.data.contains("smaller than our selected v2 reserve");
 		if !msg.data.contains("Disconnecting due to timeout awaiting response") && !is_quiescent_msg
 		{
 			panic!("Unexpected disconnect case: {}", msg.data);
@@ -817,12 +984,12 @@ struct HarnessNode<'a> {
 	logger: Arc<dyn Logger + MaybeSend + MaybeSync>,
 	broadcaster: Arc<TestBroadcaster>,
 	fee_estimator: Arc<FuzzEstimator>,
-	wallet: TestWalletSource,
+	wallet: Arc<TestWalletSource>,
+	wallet_sync: WalletSync<Arc<TestWalletSource>, Arc<dyn Logger + MaybeSend + MaybeSync>>,
 	persistence_style: ChannelMonitorUpdateStatus,
 	deferred: bool,
 	serialized_manager: Vec<u8>,
 	serialized_manager_generation: u64,
-	height: u32,
 	last_htlc_clear_fee: u32,
 }
 
@@ -866,7 +1033,7 @@ impl<'a> HarnessNode<'a> {
 	}
 
 	fn new<Out: Output + MaybeSend + MaybeSync>(
-		node_id: u8, wallet: TestWalletSource, fee_estimator: Arc<FuzzEstimator>,
+		node_id: u8, wallet: Arc<TestWalletSource>, fee_estimator: Arc<FuzzEstimator>,
 		broadcaster: Arc<TestBroadcaster>, persistence_style: ChannelMonitorUpdateStatus,
 		deferred: bool, out: &Out, router: &'a FuzzRouter, chan_type: ChanType,
 	) -> Self {
@@ -890,6 +1057,7 @@ impl<'a> HarnessNode<'a> {
 			&persister,
 			deferred,
 		);
+		let wallet_sync = WalletSync::new(Arc::clone(&wallet), Arc::clone(&logger));
 		let network = Network::Bitcoin;
 		let best_block_timestamp = genesis_block(network).header.time;
 		let params = ChainParameters { network, best_block: BlockLocator::from_network(network) };
@@ -917,11 +1085,11 @@ impl<'a> HarnessNode<'a> {
 			broadcaster,
 			fee_estimator,
 			wallet,
+			wallet_sync,
 			persistence_style,
 			deferred,
 			serialized_manager: Vec::new(),
 			serialized_manager_generation: 0,
-			height: 0,
 			last_htlc_clear_fee: 253,
 		}
 	}
@@ -958,22 +1126,77 @@ impl<'a> HarnessNode<'a> {
 		}
 	}
 
+	fn manager_height(&self) -> u32 {
+		self.node.current_best_block().height
+	}
+
+	// Connects a block range to ChainMonitor and ChannelManager. The start
+	// heights are independent because reload may pair monitors and a manager
+	// persisted at different chain tips.
+	fn connect_chain_range(
+		&mut self, chain_state: &ChainState, monitor_start_height: u32, manager_start_height: u32,
+		target_height: u32,
+	) {
+		assert!(
+			target_height >= monitor_start_height,
+			"connect_chain_range cannot move monitor height backward ({} -> {})",
+			monitor_start_height,
+			target_height
+		);
+		assert!(
+			target_height >= manager_start_height,
+			"connect_chain_range cannot move manager height backward ({} -> {})",
+			manager_start_height,
+			target_height
+		);
+		let start_height = cmp::min(monitor_start_height, manager_start_height);
+		let mut height = start_height;
+		while height < target_height {
+			let mut next_height = height + 1;
+			while next_height <= target_height && chain_state.block_at(next_height).1.is_empty() {
+				next_height += 1;
+			}
+			if next_height > target_height {
+				// The rest of the range is empty. One best-block update to the
+				// final height is enough because LDK's Confirm API explicitly
+				// allows best_block_updated to skip intermediary blocks.
+				height = target_height;
+				let (header, _) = chain_state.block_at(height);
+				if height > monitor_start_height {
+					self.monitor.best_block_updated(header, height);
+				}
+				if height > manager_start_height {
+					self.node.best_block_updated(header, height);
+				}
+				break;
+			}
+			height = next_height;
+			let (header, txn) = chain_state.block_at(height);
+			let txdata: Vec<_> = txn.iter().enumerate().map(|(i, tx)| (i + 1, tx)).collect();
+			if height > monitor_start_height {
+				self.monitor.transactions_confirmed(header, &txdata, height);
+			}
+			if height > manager_start_height {
+				self.node.transactions_confirmed(header, &txdata, height);
+			}
+			if height > monitor_start_height {
+				self.monitor.best_block_updated(header, height);
+			}
+			if height > manager_start_height {
+				self.node.best_block_updated(header, height);
+			}
+		}
+	}
+
 	fn sync_with_chain_state(&mut self, chain_state: &ChainState, num_blocks: Option<u32>) {
 		let target_height = if let Some(num_blocks) = num_blocks {
-			std::cmp::min(self.height + num_blocks, chain_state.tip_height())
+			std::cmp::min(self.manager_height() + num_blocks, chain_state.tip_height())
 		} else {
 			chain_state.tip_height()
 		};
 
-		while self.height < target_height {
-			self.height += 1;
-			let (header, txn) = chain_state.block_at(self.height);
-			let txdata: Vec<_> = txn.iter().enumerate().map(|(i, tx)| (i + 1, tx)).collect();
-			if !txdata.is_empty() {
-				self.node.transactions_confirmed(header, &txdata, self.height);
-			}
-			self.node.best_block_updated(header, self.height);
-		}
+		let start_height = self.manager_height();
+		self.connect_chain_range(chain_state, start_height, start_height, target_height);
 	}
 
 	fn checkpoint_manager_persistence(&mut self) -> bool {
@@ -1034,7 +1257,6 @@ impl<'a> HarnessNode<'a> {
 	}
 
 	fn splice_in(&self, counterparty_node_id: &PublicKey, channel_id: &ChannelId) {
-		let wallet = WalletSync::new(&self.wallet, Arc::clone(&self.logger));
 		match self.node.splice_channel(channel_id, counterparty_node_id) {
 			Ok(funding_template) => {
 				let feerate =
@@ -1043,7 +1265,7 @@ impl<'a> HarnessNode<'a> {
 					Amount::from_sat(10_000),
 					feerate,
 					FeeRate::MAX,
-					&wallet,
+					&self.wallet_sync,
 				) {
 					let _ = self.node.funding_contributed(
 						channel_id,
@@ -2125,7 +2347,7 @@ fn make_channel(
 					tx.clone(),
 				)
 				.unwrap();
-			chain_state.confirm_tx(tx);
+			chain_state.mine_setup_tx_to_depth(tx, ANTI_REORG_DELAY);
 		} else {
 			panic!("Wrong event type");
 		}
@@ -2242,24 +2464,27 @@ impl<'a, Out: Output + MaybeSend + MaybeSync> Harness<'a, Out> {
 			config_byte & 0b1000_0000 != 0,
 		];
 
-		let wallet_a = TestWalletSource::new(SecretKey::from_slice(&[1; 32]).unwrap());
-		let wallet_b = TestWalletSource::new(SecretKey::from_slice(&[2; 32]).unwrap());
-		let wallet_c = TestWalletSource::new(SecretKey::from_slice(&[3; 32]).unwrap());
-		let wallets = [&wallet_a, &wallet_b, &wallet_c];
-		let coinbase_tx = bitcoin::Transaction {
-			version: bitcoin::transaction::Version::TWO,
-			lock_time: bitcoin::absolute::LockTime::ZERO,
-			input: vec![bitcoin::TxIn { ..Default::default() }],
-			output: wallets
-				.iter()
-				.map(|wallet| TxOut {
-					value: Amount::from_sat(100_000),
-					script_pubkey: wallet.get_change_script().unwrap(),
-				})
-				.collect(),
-		};
-		for (idx, wallet) in wallets.iter().enumerate() {
-			wallet.add_utxo(coinbase_tx.clone(), idx as u32);
+		let wallet_a = Arc::new(TestWalletSource::new(SecretKey::from_slice(&[1; 32]).unwrap()));
+		let wallet_b = Arc::new(TestWalletSource::new(SecretKey::from_slice(&[2; 32]).unwrap()));
+		let wallet_c = Arc::new(TestWalletSource::new(SecretKey::from_slice(&[3; 32]).unwrap()));
+		let wallets = [wallet_a.as_ref(), wallet_b.as_ref(), wallet_c.as_ref()];
+		let mut chain_state = ChainState::new();
+		for wallet in wallets {
+			let coinbase_tx = bitcoin::Transaction {
+				version: bitcoin::transaction::Version::TWO,
+				lock_time: bitcoin::absolute::LockTime::ZERO,
+				input: vec![bitcoin::TxIn { ..Default::default() }],
+				output: (0..NUM_WALLET_UTXOS)
+					.map(|_| TxOut {
+						value: Amount::from_sat(100_000),
+						script_pubkey: wallet.get_change_script().unwrap(),
+					})
+					.collect(),
+			};
+			for vout in 0..NUM_WALLET_UTXOS {
+				wallet.add_utxo(coinbase_tx.clone(), vout);
+			}
+			chain_state.mine_setup_tx_to_depth(coinbase_tx, ANTI_REORG_DELAY);
 		}
 
 		let fee_est_a = Arc::new(FuzzEstimator { ret_val: atomic::AtomicU32::new(253) });
@@ -2274,7 +2499,7 @@ impl<'a, Out: Output + MaybeSend + MaybeSync> Harness<'a, Out> {
 		let mut nodes = [
 			HarnessNode::new(
 				0,
-				wallet_a,
+				Arc::clone(&wallet_a),
 				Arc::clone(&fee_est_a),
 				Arc::clone(&broadcast_a),
 				persistence_styles[0],
@@ -2285,7 +2510,7 @@ impl<'a, Out: Output + MaybeSend + MaybeSync> Harness<'a, Out> {
 			),
 			HarnessNode::new(
 				1,
-				wallet_b,
+				Arc::clone(&wallet_b),
 				Arc::clone(&fee_est_b),
 				Arc::clone(&broadcast_b),
 				persistence_styles[1],
@@ -2296,7 +2521,7 @@ impl<'a, Out: Output + MaybeSend + MaybeSync> Harness<'a, Out> {
 			),
 			HarnessNode::new(
 				2,
-				wallet_c,
+				Arc::clone(&wallet_c),
 				Arc::clone(&fee_est_c),
 				Arc::clone(&broadcast_c),
 				persistence_styles[2],
@@ -2306,8 +2531,6 @@ impl<'a, Out: Output + MaybeSend + MaybeSync> Harness<'a, Out> {
 				chan_type,
 			),
 		];
-		let mut chain_state = ChainState::new();
-
 		// Connect peers first, then create channels.
 		connect_peers(&nodes[0], &nodes[1]);
 		connect_peers(&nodes[1], &nodes[2]);
@@ -2376,7 +2599,34 @@ impl<'a, Out: Output + MaybeSend + MaybeSync> Harness<'a, Out> {
 		self.bc_link.first_channel_id()
 	}
 
-	fn finish(&self) {
+	// Runs end-of-input cleanup by relaying and mining remaining broadcasts.
+	// Final invariants should not depend on the input ending with explicit relay
+	// and mining bytes.
+	fn finish(&mut self) {
+		for _ in 0..MAX_FINISH_RELAY_MINE_ROUNDS {
+			let mut txs = Vec::new();
+			for node in &self.nodes {
+				txs.extend(node.broadcaster.txn_broadcasted.borrow_mut().drain(..));
+			}
+			self.chain_state.relay_transactions(txs);
+			if self.chain_state.pending_txs.is_empty() {
+				assert_test_invariants(&self.nodes);
+				return;
+			}
+			if self.mine_blocks(ANTI_REORG_DELAY) == 0 {
+				// The input ended with pending mempool transactions but no safe
+				// block left before an HTLC fail-back window. Leave them
+				// unconfirmed rather than forcing finish cleanup to advance
+				// the chain past that boundary.
+				assert_test_invariants(&self.nodes);
+				return;
+			}
+		}
+		assert!(
+			!self.nodes.iter().any(|node| !node.broadcaster.txn_broadcasted.borrow().is_empty())
+				&& self.chain_state.pending_txs.is_empty(),
+			"finish tx mining loop failed to quiesce",
+		);
 		assert_test_invariants(&self.nodes);
 	}
 
@@ -2775,8 +3025,8 @@ impl<'a, Out: Output + MaybeSend + MaybeSync> Harness<'a, Out> {
 
 	fn process_events(&mut self, node_idx: usize, fail: bool) -> bool {
 		let nodes = &self.nodes;
-		let chain_state = &mut self.chain_state;
 		let payments = &mut self.payments;
+		let chain_state = &self.chain_state;
 		// Multiple HTLCs can resolve for the same payment hash, so deduplicate
 		// claim/fail handling per event batch.
 		let mut claim_set = new_hash_map();
@@ -2814,29 +3064,53 @@ impl<'a, Out: Output + MaybeSend + MaybeSync> Harness<'a, Out> {
 					unsigned_transaction,
 					..
 				} => {
-					let signed_tx = nodes[node_idx].wallet.sign_tx(unsigned_transaction).unwrap();
-					match nodes[node_idx].funding_transaction_signed(
-						&channel_id,
-						&counterparty_node_id,
-						signed_tx,
-					) {
-						Ok(()) => {},
-						Err(APIError::APIMisuseError { ref err })
-							if err.contains("not expecting funding signatures") =>
+					let wallet_script = nodes[node_idx].wallet.get_change_script().unwrap();
+					let has_unknown_spent_input = unsigned_transaction.input.iter().any(|input| {
+						!chain_state.is_unspent(&input.previous_output)
+							&& chain_state.confirmed_output(&input.previous_output).is_none()
+					});
+					assert!(
+						!has_unknown_spent_input,
+						"funding transaction referenced an unmodeled input: {:?}",
+						unsigned_transaction,
+					);
+					let has_spent_wallet_input = unsigned_transaction.input.iter().any(|input| {
+						!chain_state.is_unspent(&input.previous_output)
+							&& chain_state
+								.confirmed_output(&input.previous_output)
+								.map_or(false, |output| output.script_pubkey == wallet_script)
+					});
+					if has_spent_wallet_input {
+						// A queued RBF signing request can lose the race against a
+						// transaction confirming with one of its wallet inputs.
+						match nodes[node_idx]
+							.cancel_funding_contributed(&channel_id, &counterparty_node_id)
 						{
-							// A queued signing event can be invalidated by a later `tx_abort`
-							// before the application handles it.
-						},
-						Err(e) => panic!("{e:?}"),
+							Ok(()) => {},
+							Err(APIError::APIMisuseError { ref err })
+								if err.contains("does not have a pending splice negotiation") => {},
+							Err(e) => panic!("{e:?}"),
+						}
+					} else {
+						let signed_tx =
+							nodes[node_idx].wallet.sign_tx(unsigned_transaction).unwrap();
+						match nodes[node_idx].funding_transaction_signed(
+							&channel_id,
+							&counterparty_node_id,
+							signed_tx,
+						) {
+							Ok(()) => {},
+							Err(APIError::APIMisuseError { ref err })
+								if err.contains("not expecting funding signatures") =>
+							{
+								// A queued signing event can be invalidated by a later `tx_abort`
+								// before the application handles it.
+							},
+							Err(e) => panic!("{e:?}"),
+						}
 					}
 				},
-				events::Event::SpliceNegotiated { new_funding_txo, .. } => {
-					let mut txs = nodes[node_idx].broadcaster.txn_broadcasted.borrow_mut();
-					assert!(txs.len() >= 1);
-					let splice_tx = txs.remove(0);
-					assert_eq!(new_funding_txo.txid, splice_tx.compute_txid());
-					chain_state.add_pending_tx(splice_tx);
-				},
+				events::Event::SpliceNegotiated { .. } => {},
 				events::Event::SpliceNegotiationFailed { .. } => {},
 				events::Event::DiscardFunding {
 					funding_info:
@@ -2935,6 +3209,20 @@ impl<'a, Out: Output + MaybeSend + MaybeSync> Harness<'a, Out> {
 		self.bc_link.reconnect(&self.nodes);
 	}
 
+	// Finds the earliest loaded monitor height for a node. Startup sync uses it
+	// as ChainMonitor's start height so raw monitors loaded below the manager's
+	// best block still see every block and transaction they missed.
+	fn oldest_monitor_height_for_node(&self, node_idx: usize) -> u32 {
+		let node = &self.nodes[node_idx];
+		let mut min_monitor_height = node.manager_height();
+		for chan_id in node.monitor.list_monitors() {
+			if let Ok(mon) = node.monitor.get_monitor(chan_id) {
+				min_monitor_height = cmp::min(min_monitor_height, mon.current_best_block().height);
+			}
+		}
+		min_monitor_height
+	}
+
 	fn restart_node(&mut self, node_idx: usize, v: u8, router: &'a FuzzRouter) {
 		if !self.nodes[node_idx].deferred {
 			self.nodes[node_idx].checkpoint_manager_persistence();
@@ -2954,6 +3242,21 @@ impl<'a, Out: Output + MaybeSend + MaybeSync> Harness<'a, Out> {
 		}
 		let loaded_manager_generation =
 			self.nodes[node_idx].reload(v, &self.out, router, self.chan_type);
+		let monitor_start_height = self.oldest_monitor_height_for_node(node_idx);
+		let manager_start_height = self.nodes[node_idx].manager_height();
+		// Startup sync is part of LDK's deserialization contract.
+		self.nodes[node_idx].connect_chain_range(
+			&self.chain_state,
+			monitor_start_height,
+			manager_start_height,
+			self.chain_state.tip_height(),
+		);
+		assert_eq!(
+			self.nodes[node_idx].manager_height(),
+			self.chain_state.tip_height(),
+			"reloaded node {} must sync to the harness tip before normal operation resumes",
+			node_idx
+		);
 		let rolled_back_payment_hashes = self.payments.nodes[node_idx]
 			.sync_pending_with_manager_generation(loaded_manager_generation);
 		for payment_hash in rolled_back_payment_hashes {
@@ -2962,6 +3265,11 @@ impl<'a, Out: Output + MaybeSend + MaybeSync> Harness<'a, Out> {
 	}
 
 	fn settle_all(&mut self) {
+		let chain_state = &self.chain_state;
+		for node in &mut self.nodes {
+			node.sync_with_chain_state(chain_state, None);
+		}
+
 		// First, make sure peers are all connected to each other
 		self.reconnect_ab();
 		self.reconnect_bc();
@@ -3036,6 +3344,102 @@ impl<'a, Out: Output + MaybeSend + MaybeSync> Harness<'a, Out> {
 		}
 		made_progress
 	}
+
+	// Relays one node's broadcasts into the mempool. Per-node relay lets fuzz
+	// inputs model partial propagation before a block is mined.
+	fn relay_broadcasts_for_node(&mut self, node_idx: usize) {
+		let txs = self.nodes[node_idx]
+			.broadcaster
+			.txn_broadcasted
+			.borrow_mut()
+			.drain(..)
+			.collect::<Vec<_>>();
+		self.chain_state.relay_transactions(txs);
+	}
+
+	fn earliest_pending_htlc_expiry(&self) -> Option<u32> {
+		let mut earliest_expiry: Option<u32> = None;
+		for node in &self.nodes {
+			for chan in node.list_channels() {
+				for htlc in &chan.pending_inbound_htlcs {
+					earliest_expiry = Some(
+						earliest_expiry
+							.map_or(htlc.cltv_expiry, |expiry| expiry.min(htlc.cltv_expiry)),
+					);
+				}
+				for htlc in &chan.pending_outbound_htlcs {
+					earliest_expiry = Some(
+						earliest_expiry
+							.map_or(htlc.cltv_expiry, |expiry| expiry.min(htlc.cltv_expiry)),
+					);
+				}
+			}
+		}
+		earliest_expiry
+	}
+
+	fn safe_mine_block_count(&self, count: u32) -> u32 {
+		if let Some(expiry) = self.earliest_pending_htlc_expiry() {
+			let current_tip = self.chain_state.tip_height();
+			// LDK may close to protect a pending HTLC before its raw CLTV
+			// expiry. Keep mining outside that fail-back window so fuzzed block
+			// production does not force an on-chain timeout path.
+			let timeout_deadline = expiry.saturating_sub(channelmonitor::HTLC_FAIL_BACK_BUFFER);
+			assert!(
+				current_tip < timeout_deadline,
+				"pending HTLC with expiry {} and timeout deadline {} is already unsafe at tip {}",
+				expiry,
+				timeout_deadline,
+				current_tip
+			);
+			// Stop before the deadline block itself, since connecting it is
+			// enough for ChannelMonitor timeout handling to run.
+			count.min(timeout_deadline - current_tip - 1)
+		} else {
+			count
+		}
+	}
+
+	// Mines blocks through ChainState, then applies confirmed transactions to
+	// the wallets and syncs node chain listeners.
+	fn mine_blocks(&mut self, count: u32) -> u32 {
+		assert!(count > 0, "mining zero blocks should not be requested");
+
+		let count = self.safe_mine_block_count(count);
+		if count == 0 {
+			return 0;
+		}
+		let confirmed_txs = self.chain_state.mine_blocks(count);
+		let wallets = [
+			self.nodes[0].wallet.as_ref(),
+			self.nodes[1].wallet.as_ref(),
+			self.nodes[2].wallet.as_ref(),
+		];
+		for tx in &confirmed_txs {
+			for wallet in wallets.iter().copied() {
+				let change_script = wallet.get_change_script().unwrap();
+				for input in &tx.input {
+					// The test wallet is a simple UTXO source. When one of its
+					// outputs is spent by a confirmed transaction, remove it so
+					// later funding attempts cannot double-spend it.
+					wallet.remove_utxo(input.previous_output);
+				}
+				for (vout, output) in tx.output.iter().enumerate() {
+					if output.script_pubkey == change_script {
+						// Add outputs to whichever test wallet owns the script.
+						// This lets splice flows recycle wallet change through
+						// later fuzz commands.
+						wallet.add_utxo(tx.clone(), vout as u32);
+					}
+				}
+			}
+		}
+		let chain_state = &self.chain_state;
+		for node in &mut self.nodes {
+			node.sync_with_chain_state(chain_state, None);
+		}
+		count
+	}
 }
 
 #[inline]
@@ -3245,32 +3649,14 @@ pub fn do_test<Out: Output + MaybeSend + MaybeSync>(data: &[u8], out: Out) {
 				harness.nodes[2].splice_out(&cp_node_id, &harness.chan_b_id());
 			},
 
-			// Sync node by 1 block to cover confirmation of a transaction.
-			0xa8 => {
-				harness.chain_state.confirm_pending_txs();
-				harness.nodes[0].sync_with_chain_state(&harness.chain_state, Some(1));
-			},
-			0xa9 => {
-				harness.chain_state.confirm_pending_txs();
-				harness.nodes[1].sync_with_chain_state(&harness.chain_state, Some(1));
-			},
-			0xaa => {
-				harness.chain_state.confirm_pending_txs();
-				harness.nodes[2].sync_with_chain_state(&harness.chain_state, Some(1));
-			},
-			// Sync node to chain tip to cover confirmation of a transaction post-reorg-risk.
-			0xab => {
-				harness.chain_state.confirm_pending_txs();
-				harness.nodes[0].sync_with_chain_state(&harness.chain_state, None);
-			},
-			0xac => {
-				harness.chain_state.confirm_pending_txs();
-				harness.nodes[1].sync_with_chain_state(&harness.chain_state, None);
-			},
-			0xad => {
-				harness.chain_state.confirm_pending_txs();
-				harness.nodes[2].sync_with_chain_state(&harness.chain_state, None);
-			},
+			// Sync node by 1 block.
+			0xa8 => harness.nodes[0].sync_with_chain_state(&harness.chain_state, Some(1)),
+			0xa9 => harness.nodes[1].sync_with_chain_state(&harness.chain_state, Some(1)),
+			0xaa => harness.nodes[2].sync_with_chain_state(&harness.chain_state, Some(1)),
+			// Sync node to chain tip.
+			0xab => harness.nodes[0].sync_with_chain_state(&harness.chain_state, None),
+			0xac => harness.nodes[1].sync_with_chain_state(&harness.chain_state, None),
+			0xad => harness.nodes[2].sync_with_chain_state(&harness.chain_state, None),
 
 			0xb0 | 0xb1 | 0xb2 => {
 				// Restart node A, picking among persisted and in-flight `ChannelMonitor`
@@ -3395,6 +3781,13 @@ pub fn do_test<Out: Output + MaybeSend + MaybeSync>(data: &[u8], out: Out) {
 					.enable_op_for_all_signers(SignerOp::SignSpliceSharedInput);
 				harness.nodes[2].signer_unblocked(None);
 			},
+			0xd6 => harness.relay_broadcasts_for_node(0),
+			0xd7 => harness.relay_broadcasts_for_node(1),
+			0xd8 => harness.relay_broadcasts_for_node(2),
+			0xd9..=0xe0 => {
+				let count = MINE_BLOCK_COUNTS[(v - 0xd9) as usize];
+				harness.mine_blocks(count);
+			},
 
 			0xf0 => harness.ab_link.complete_monitor_updates_for_node(
 				0,
diff --git a/lightning/src/ln/channel.rs b/lightning/src/ln/channel.rs
index 3df6f5fc436..463c2e8e8f6 100644
--- a/lightning/src/ln/channel.rs
+++ b/lightning/src/ln/channel.rs
@@ -12786,6 +12786,17 @@ where
 			));
 		}
 
+		if pending_splice
+			.negotiated_candidates
+			.iter()
+			.any(|funding| funding.funding_tx_confirmation_height != 0)
+		{
+			return Err(format!(
+				"Channel {} has a confirmed pending splice, cannot RBF",
+				self.context.channel_id(),
+			));
+		}
+
 		if pending_splice.negotiated_candidates.is_empty() {
 			return Err(format!(
 				"Channel {} has no negotiated splice candidates to RBF",
@@ -13438,6 +13449,17 @@ where
 			)));
 		}
 
+		if pending_splice
+			.negotiated_candidates
+			.iter()
+			.any(|funding| funding.funding_tx_confirmation_height != 0)
+		{
+			return Err(ChannelError::WarnAndDisconnect(format!(
+				"Channel {} has a confirmed pending splice, cannot RBF",
+				self.context.channel_id(),
+			)));
+		}
+
 		let last_candidate = match pending_splice.negotiated_candidates.last() {
 			Some(candidate) => candidate,
 			None => {