Add LSPS2 replay regression coverage

Persisting LSPS2 service state can race with replayed intercepted HTLC
events after restart. Cover replaying the same intercepted HTLC after
restoring peer state so duplicate queueing is caught.

Co-Authored-By: HAL 9000

Author: tnull

lightning-liquidity/src/lsps2/service.rs

@@ -2361,6 +2361,8 @@ mod tests {
 
 	use bitcoin::{absolute::LockTime, transaction::Version};
 	use core::str::FromStr;
+	use lightning::io::Cursor;
+	use lightning::util::ser::{Readable, Writeable};
 
 	const MAX_VALUE_MSAT: u64 = 21_000_000_0000_0000_000;
 
@@ -2764,6 +2766,52 @@ mod tests {
 		}
 	}
 
+	#[test]
+	fn replayed_intercepted_htlc_after_persist_is_idempotent() {
+		let payment_size_msat = Some(500_000_000);
+		let opening_fee_params = LSPS2OpeningFeeParams {
+			min_fee_msat: 10_000_000,
+			proportional: 10_000,
+			valid_until: LSPSDateTime::from_str("2035-05-20T08:30:45Z").unwrap(),
+			min_lifetime: 4032,
+			max_client_to_self_delay: 2016,
+			min_payment_size_msat: 10_000_000,
+			max_payment_size_msat: 1_000_000_000,
+			promise: "ignore".to_string(),
+		};
+		let intercept_scid = 42;
+		let user_channel_id = 43;
+		let htlc = InterceptedHTLC {
+			intercept_id: InterceptId([1; 32]),
+			expected_outbound_amount_msat: 500_000_000,
+			payment_hash: PaymentHash([2; 32]),
+		};
+
+		let mut jit_channel =
+			OutboundJITChannel::new(payment_size_msat, opening_fee_params, user_channel_id, false);
+		assert!(matches!(
+			jit_channel.htlc_intercepted(htlc).unwrap(),
+			Some(HTLCInterceptedAction::OpenChannel(_))
+		));
+
+		let mut peer_state = PeerState::new();
+		peer_state.intercept_scid_by_user_channel_id.insert(user_channel_id, intercept_scid);
+		peer_state.insert_outbound_channel(intercept_scid, jit_channel);
+
+		let encoded_peer_state = peer_state.encode();
+		let mut decoded_peer_state = PeerState::read(&mut Cursor::new(encoded_peer_state)).unwrap();
+		let decoded_jit_channel = decoded_peer_state
+			.outbound_channels_by_intercept_scid
+			.get_mut(&intercept_scid)
+			.unwrap();
+
+		assert!(decoded_jit_channel.htlc_intercepted(htlc).unwrap().is_none());
+
+		let ForwardPaymentAction(_, fee_payment) =
+			decoded_jit_channel.channel_ready(ChannelId([3; 32])).unwrap();
+		assert_eq!(fee_payment.htlcs, vec![htlc]);
+	}
+
 	#[test]
 	fn broadcast_not_allowed_after_non_paying_fee_payment_claimed() {
 		let min_fee_msat: u64 = 12345;