Implement background job for transaction rebroadcasting

Introduces a `RebroadcastPolicy` to manage the automatic rebroadcasting
of unconfirmed transactions with exponential backoff. This prevents
excessive network spam while systematically retrying stuck transactions.

The feature is enabled by default but can be disabled via the builder:
`builder.set_auto_rebroadcast_unconfirmed(false)`.

Configuration options:
- min_rebroadcast_interval: Base delay between attempts (seconds)
- max_broadcast_attempts: Total attempts before abandonment
- backoff_factor: Multiplier for exponential delay increase

Sensible defaults are provided (300s, 24 attempts, 1.5x backoff).

Author: Camillarhi

src/wallet/mod.rs

@@ -29,6 +29,7 @@ use bitcoin::{
 	Address, Amount, FeeRate, OutPoint, ScriptBuf, Transaction, TxOut, Txid, WPubkeyHash, Weight,
 	WitnessProgram, WitnessVersion,
 };
+
 use lightning::chain::chaininterface::BroadcasterInterface;
 use lightning::chain::channelmonitor::ANTI_REORG_DELAY;
 use lightning::chain::{BestBlock, Listen};
@@ -244,31 +245,54 @@ impl Wallet {
 					self.pending_payment_store.insert_or_update(pending_payment)?;
 				},
 				WalletEvent::ChainTipChanged { new_tip, .. } => {
-					// Get all payments that are Pending with Confirmed status
+					// Get all on-chain payments that are Pending
 					let pending_payments: Vec<PendingPaymentDetails> =
 						self.pending_payment_store.list_filter(|p| {
 							p.details.status == PaymentStatus::Pending
-								&& matches!(
-									p.details.kind,
-									PaymentKind::Onchain {
-										status: ConfirmationStatus::Confirmed { .. },
-										..
-									}
-								)
+								&& matches!(p.details.kind, PaymentKind::Onchain { .. })
 						});
 
+					let mut unconfirmed_outbound_txids: Vec<Txid> = Vec::new();
+
 					for mut payment in pending_payments {
-						if let PaymentKind::Onchain {
-							status: ConfirmationStatus::Confirmed { height, .. },
-							..
-						} = payment.details.kind
-						{
-							let payment_id = payment.details.id;
-							if new_tip.height >= height + ANTI_REORG_DELAY - 1 {
-								payment.details.status = PaymentStatus::Succeeded;
-								self.payment_store.insert_or_update(payment.details)?;
-								self.pending_payment_store.remove(&payment_id)?;
-							}
+						match payment.details.kind {
+							PaymentKind::Onchain {
+								status: ConfirmationStatus::Confirmed { height, .. },
+								..
+							} => {
+								let payment_id = payment.details.id;
+								if new_tip.height >= height + ANTI_REORG_DELAY - 1 {
+									payment.details.status = PaymentStatus::Succeeded;
+									self.payment_store.insert_or_update(payment.details)?;
+									self.pending_payment_store.remove(&payment_id)?;
+								}
+							},
+							PaymentKind::Onchain {
+								txid,
+								status: ConfirmationStatus::Unconfirmed,
+							} if payment.details.direction == PaymentDirection::Outbound => {
+								unconfirmed_outbound_txids.push(txid);
+							},
+							_ => {},
+						}
+					}
+
+					if !unconfirmed_outbound_txids.is_empty() {
+						let txs_to_broadcast: Vec<Transaction> = unconfirmed_outbound_txids
+							.iter()
+							.filter_map(|txid| {
+								locked_wallet.tx_details(*txid).map(|d| (*d.tx).clone())
+							})
+							.collect();
+
+						if !txs_to_broadcast.is_empty() {
+							let tx_refs: Vec<&Transaction> = txs_to_broadcast.iter().collect();
+							self.broadcaster.broadcast_transactions(&tx_refs);
+							log_info!(
+								self.logger,
+								"Rebroadcast {} unconfirmed transactions on chain tip change",
+								txs_to_broadcast.len()
+							);
 						}
 					}
 				},