Implement RBF fee bumping for unconfirmed transactions

Add `Replace-by-Fee` functionality to allow users to increase fees on
pending outbound transactions, improving confirmation likelihood during
network congestion.

- Uses BDK's `build_fee_bump` for transaction replacement
- Validates transaction eligibility: must be outbound and unconfirmed
- Implements fee rate estimation with safety limits
- Maintains payment history consistency across wallet updates
- Includes integration tests for various RBF scenarios

Author: Camillarhi

bindings/ldk_node.udl

@@ -269,6 +269,8 @@ interface OnchainPayment {
 	Txid send_all_to_address([ByRef]Address address, boolean retain_reserve, FeeRate? fee_rate);
 	[Throws=NodeError]
 	void rebroadcast_transaction(PaymentId payment_id);
+	[Throws=NodeError]
+	Txid bump_fee_rbf(PaymentId payment_id);
 };
 
 interface FeeRate {

src/payment/onchain.rs

@@ -17,11 +17,8 @@ use crate::logger::{log_info, LdkLogger, Logger};
 use crate::types::{ChannelManager, Wallet};
 use crate::wallet::OnchainSendAmount;
 
-use bitcoin::{Address, Txid};
 use lightning::ln::channelmanager::PaymentId;
 
-use std::sync::{Arc, RwLock};
-
 #[cfg(not(feature = "uniffi"))]
 type FeeRate = bitcoin::FeeRate;
 #[cfg(feature = "uniffi")]
@@ -136,4 +133,18 @@ impl OnchainPayment {
 	pub fn rebroadcast_transaction(&self, payment_id: PaymentId) -> Result<(), Error> {
 		self.wallet.rebroadcast_transaction(payment_id)
 	}
+
+	/// Attempt to bump the fee of an unconfirmed transaction using Replace-by-Fee (RBF).
+	///
+	/// This creates a new transaction that replaces the original one, increasing the fee by the
+	/// specified increment to improve its chances of confirmation. The original transaction must
+	/// be signaling RBF replaceability for this to succeed.
+	///
+	/// The new transaction will have the same outputs as the original but with a
+	/// higher fee, resulting in faster confirmation potential.
+	///
+	/// Returns the Txid of the new replacement transaction if successful.
+	pub fn bump_fee_rbf(&self, payment_id: PaymentId) -> Result<Txid, Error> {
+		self.wallet.bump_fee_rbf(payment_id)
+	}
 }

src/payment/pending_payment_store.rs

@@ -62,9 +62,12 @@ impl StorableObject for PendingPaymentDetails {
 		}
 
 		if let Some(new_conflicting_txids) = &update.conflicting_txids {
-			if &self.conflicting_txids != new_conflicting_txids {
-				self.conflicting_txids = new_conflicting_txids.clone();
-				updated = true;
+			// Don't overwrite existing conflicts with an empty list
+			if !new_conflicting_txids.is_empty() {
+				if &self.conflicting_txids != new_conflicting_txids {
+					self.conflicting_txids = new_conflicting_txids.clone();
+					updated = true;
+				}
 			}
 		}
 

src/payment/store.rs

@@ -7,7 +7,7 @@
 
 use std::time::{Duration, SystemTime, UNIX_EPOCH};
 
-use bitcoin::{BlockHash, Txid};
+use bitcoin::{BlockHash, Transaction, Txid};
 use lightning::ln::channelmanager::PaymentId;
 use lightning::ln::msgs::DecodeError;
 use lightning::offers::offer::OfferId;
@@ -19,10 +19,6 @@ use lightning::{
 use lightning_types::payment::{PaymentHash, PaymentPreimage, PaymentSecret};
 use lightning_types::string::UntrustedString;
 
-use bitcoin::{BlockHash, Transaction, Txid};
-
-use std::time::{Duration, SystemTime, UNIX_EPOCH};
-
 use crate::data_store::{StorableObject, StorableObjectId, StorableObjectUpdate};
 use crate::hex_utils;
 
@@ -322,6 +318,15 @@ impl StorableObject for PaymentDetails {
 			}
 		}
 
+		if let Some(tx_id) = update.txid {
+			match self.kind {
+				PaymentKind::Onchain { ref mut txid, .. } => {
+					update_if_necessary!(*txid, tx_id);
+				},
+				_ => {},
+			}
+		}
+
 		if updated {
 			self.latest_update_timestamp = SystemTime::now()
 				.duration_since(UNIX_EPOCH)
@@ -583,6 +588,7 @@ pub(crate) struct PaymentDetailsUpdate {
 	pub raw_tx: Option<Option<Transaction>>,
 	pub last_broadcast_time: Option<Option<u64>>,
 	pub broadcast_attempts: Option<Option<u32>>,
+	pub txid: Option<Txid>,
 }
 
 impl PaymentDetailsUpdate {
@@ -601,6 +607,7 @@ impl PaymentDetailsUpdate {
 			raw_tx: None,
 			last_broadcast_time: None,
 			broadcast_attempts: None,
+			txid: None,
 		}
 	}
 }
@@ -616,16 +623,23 @@ impl From<&PaymentDetails> for PaymentDetailsUpdate {
 			_ => (None, None, None),
 		};
 
-		let (confirmation_status, raw_tx, last_broadcast_time, broadcast_attempts) =
+		let (confirmation_status, raw_tx, last_broadcast_time, broadcast_attempts, txid) =
 			match &value.kind {
 				PaymentKind::Onchain {
 					status,
 					raw_tx,
 					last_broadcast_time,
 					broadcast_attempts,
+					txid,
 					..
-				} => (Some(*status), raw_tx.clone(), *last_broadcast_time, *broadcast_attempts),
-				_ => (None, None, None, None),
+				} => (
+					Some(*status),
+					raw_tx.clone(),
+					*last_broadcast_time,
+					*broadcast_attempts,
+					Some(*txid),
+				),
+				_ => (None, None, None, None, None),
 			};
 
 		let counterparty_skimmed_fee_msat = match value.kind {
@@ -649,6 +663,7 @@ impl From<&PaymentDetails> for PaymentDetailsUpdate {
 			raw_tx: Some(raw_tx),
 			last_broadcast_time: Some(last_broadcast_time),
 			broadcast_attempts: Some(broadcast_attempts),
+			txid,
 		}
 	}
 }