test(cbf): wait for Kyoto to catch up to bitcoind after mining

generate_blocks_and_wait only waits for electrsd. Add
sync_node_to_bitcoind_tip so close-cycle tests stop needing the
unconditional double sync_wallets workaround.

Author: febyeji

tests/common/mod.rs

@@ -608,6 +608,37 @@ pub(crate) async fn wait_for_tx<E: ElectrumApi>(electrs: &E, txid: Txid) {
 	.await;
 }
 
+/// Keep calling `sync_wallets()` until the node's chain tip catches up to
+/// bitcoind's current tip, or panic if it doesn't converge within the timeout.
+///
+/// `generate_blocks_and_wait` only waits for electrsd to observe the new
+/// blocks, which races with CBF's Kyoto peer receiving them via P2P. Tests
+/// that assert on post-mining state right after mining can see CBF still
+/// stuck on the previous tip; polling here lets Kyoto catch up naturally.
+/// For non-CBF chain sources the condition is typically satisfied by the
+/// very first sync, so the overhead is negligible.
+pub(crate) async fn sync_node_to_bitcoind_tip(node: &TestNode, bitcoind: &BitcoindClient) {
+	let target_height =
+		bitcoind.get_blockchain_info().expect("failed to query bitcoind blockchain info").blocks
+			as u32;
+	let mut delay = Duration::from_millis(100);
+	for _ in 0..30 {
+		let _ = node.sync_wallets();
+		if node.status().current_best_block.height >= target_height {
+			return;
+		}
+		tokio::time::sleep(delay).await;
+		if delay < Duration::from_secs(2) {
+			delay = delay.mul_f32(1.5);
+		}
+	}
+	panic!(
+		"sync_node_to_bitcoind_tip: node did not reach height {} within timeout (stuck at {})",
+		target_height,
+		node.status().current_best_block.height
+	);
+}
+
 pub(crate) async fn wait_for_outpoint_spend<E: ElectrumApi>(electrs: &E, outpoint: OutPoint) {
 	let tx = electrs.transaction_get(&outpoint.txid).unwrap();
 	let txout_script = tx.output.get(outpoint.vout as usize).unwrap().clone().script_pubkey;
@@ -1357,15 +1388,8 @@ pub(crate) async fn do_channel_full_cycle<E: ElectrumApi>(
 	wait_for_outpoint_spend(electrsd, splice_in_txo).await;
 
 	generate_blocks_and_wait(&bitcoind, electrsd, 1).await;
-	node_a.sync_wallets().unwrap();
-	node_b.sync_wallets().unwrap();
-
-	// CBF needs a second sync: the first sync confirms the close tx in the
-	// Lightning wallet, which may trigger new script registrations. The
-	// second sync picks up blocks matching those new scripts for the
-	// on-chain wallet.
-	node_a.sync_wallets().unwrap();
-	node_b.sync_wallets().unwrap();
+	sync_node_to_bitcoind_tip(&node_a, bitcoind).await;
+	sync_node_to_bitcoind_tip(&node_b, bitcoind).await;
 
 	if force_close {
 		// Check node_b properly sees all balances and sweeps them.