Fix task-slot collision when pathfinding scores sync is enabled

The pathfinding scores sync task claimed the runtime's single
background-processor slot, which LDK's background processor also claims
later during startup. With a scores sync URL configured, node startup
tripped a debug_assert in debug builds; in release builds the second
spawn silently dropped the scores-sync task's join handle, so the task
was detached and never joined at shutdown.

Spawn it as a cancellable background task instead, matching the RGS
gossip sync task, so it is cancelled with the other such tasks in
Node::stop.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: jkczyz

src/scoring.rs

@@ -26,7 +26,7 @@ pub fn setup_background_pathfinding_scores_sync(
 
 	let logger = Arc::clone(&logger);
 
-	runtime.spawn_background_processor_task(async move {
+	runtime.spawn_cancellable_background_task(async move {
 		let mut interval = tokio::time::interval(EXTERNAL_PATHFINDING_SCORES_SYNC_INTERVAL);
 		loop {
 			tokio::select! {

tests/integration_tests_rust.rs

@@ -551,6 +551,26 @@ async fn start_stop_reinit() {
 	reinitialized_node.stop().unwrap();
 }
 
+// The scores-sync task runs alongside LDK's background processor, which claims the runtime's
+// single background-processor slot; startup must not panic with both configured.
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+async fn start_stop_with_pathfinding_scores_sync() {
+	let (_bitcoind, electrsd) = setup_bitcoind_and_electrsd();
+	let config = random_config(true);
+
+	let esplora_url = format!("http://{}", electrsd.esplora_url.as_ref().unwrap());
+
+	let mut sync_config = EsploraSyncConfig::default();
+	sync_config.background_sync_config = None;
+	setup_builder!(builder, config.node_config);
+	builder.set_chain_source_esplora(esplora_url.clone(), Some(sync_config));
+	builder.set_pathfinding_scores_source(esplora_url);
+
+	let node = builder.build(config.node_entropy.into()).unwrap();
+	node.start().unwrap();
+	node.stop().unwrap();
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 1)]
 async fn onchain_send_receive() {
 	let (bitcoind, electrsd) = setup_bitcoind_and_electrsd();